Thank you Paul,
after some further testing one SDCARD reader works with the high speed SDCARDs although a bit unreliable.
The other one has the following messages produced with dmesg, I removed the reader again to be able to run dmesg. I made gab where the messages start appearing on the screen:
[ 95.242976] usb 1-1.4: new full-speed USB device number 7 using dwc_otg
[ 95.502972] usb 1-1.4: new high-speed USB device number 8 using dwc_otg
[ 95.604630] usb 1-1.4: New USB device found, idVendor=14cd, idProduct=125c
[ 95.604709] usb 1-1.4: New USB device strings: Mfr=1, Product=3, SerialNumber=2
[ 95.604731] usb 1-1.4: Product: Mass Storage Device
[ 95.604750] usb 1-1.4: Manufacturer: Generic
[ 95.604770] usb 1-1.4: SerialNumber: 125C20100726
[ 95.611452] usb-storage 1-1.4:1.0: USB Mass Storage device detected
[ 95.616249] scsi host1: usb-storage 1-1.4:1.0
[ 96.614287] scsi 1:0:0:0: Direct-Access Mass Storage Device PQ: 0 ANSI: 0 CCS
[ 96.617053] sd 1:0:0:0: [sdb] 31293440 512-byte logical blocks: (16.0 GB/14.9 GiB)
[ 96.617651] sd 1:0:0:0: [sdb] Write Protect is off
[ 96.617694] sd 1:0:0:0: [sdb] Mode Sense: 03 00 00 00
[ 96.618261] sd 1:0:0:0: [sdb] No Caching mode page found
[ 96.618302] sd 1:0:0:0: [sdb] Assuming drive cache: write through
[ 96.624886] sdb: sdb1 sdb2 sdb3
[ 96.633029] sd 1:0:0:0: [sdb] Attached SCSI removable disk
[ 99.072957] usb 1-1.4: reset high-speed USB device number 8 using dwc_otg
[ 99.273015] usb 1-1.4: reset high-speed USB device number 8 using dwc_otg
[ 99.472950] usb 1-1.4: reset high-speed USB device number 8 using dwc_otg
[ 99.673012] usb 1-1.4: reset high-speed USB device number 8 using dwc_otg
[ 99.872946] usb 1-1.4: reset high-speed USB device number 8 using dwc_otg
[ 100.073009] usb 1-1.4: reset high-speed USB device number 8 using dwc_otg
[ 100.173973] sd 1:0:0:0: [sdb] UNKNOWN(0x2003) Result: hostbyte=0x07 driverbyte=0x00
[ 100.174025] sd 1:0:0:0: [sdb] CDB: opcode=0x28 28 00 00 00 00 20 00 00 18 00
[ 100.174052] blk_update_request: I/O error, dev sdb, sector 32
[ 100.252950] usb 1-1.4: reset high-speed USB device number 8 using dwc_otg
[ 100.453051] usb 1-1.4: reset high-speed USB device number 8 using dwc_otg
[ 100.652949] usb 1-1.4: reset high-speed USB device number 8 using dwc_otg
[ 100.853042] usb 1-1.4: reset high-speed USB device number 8 using dwc_otg
[ 101.052949] usb 1-1.4: reset high-speed USB device number 8 using dwc_otg
[ 101.253005] usb 1-1.4: reset high-speed USB device number 8 using dwc_otg
[ 101.353901] sd 1:0:0:0: [sdb] UNKNOWN(0x2003) Result: hostbyte=0x07 driverbyte=0x00
[ 101.353954] sd 1:0:0:0: [sdb] CDB: opcode=0x28 28 00 00 00 00 40 00 00 38 00
[ 101.353978] blk_update_request: I/O error, dev sdb, sector 64
[ 101.432952] usb 1-1.4: reset high-speed USB device number 8 using dwc_otg
[ 101.632953] usb 1-1.4: reset high-speed USB device number 8 using dwc_otg
[ 101.832949] usb 1-1.4: reset high-speed USB device number 8 using dwc_otg
[ 106.932948] Unable to handle kernel NULL pointer dereference at virtual address 00000020
[ 106.947156] pgd = c0004000
[ 106.955749] [00000020] *pgd=00000000
[ 106.965210] Internal error: Oops: 17 [#1] PREEMPT ARM
[ 106.976166] Modules linked in: i2c_dev evdev i2c_bcm2708 spi_bcm2835 bcm2835_gpiomem regmap_mmio uio_pdrv_genirq uio
[ 106.992975] CPU: 0 PID: 1174 Comm: usb-storage Not tainted 4.1.13-piCore+ #1
[ 107.006118] Hardware name: BCM2708
[ 107.015538] task: d5a55280 ti: d59c6000 task.ti: d59c6000
[ 107.027074] PC is at dwc_otg_hcd_qh_free+0x38/0xf0
[ 107.038030] LR is at DWC_SPINLOCK_IRQSAVE+0x24/0x44
[ 107.049024] pc : [<c0437150>] lr : [<c043d95c>] psr: 00000093
[ 107.049024] sp : d59c7d18 ip : d59c7d00 fp : d59c7d3c
[ 107.072780] r10: 00000000 r9 : 00000000 r8 : 00000001
[ 107.083985] r7 : d9966c00 r6 : d58abc60 r5 : d58abc68 r4 : 00000000
[ 107.096413] r3 : d59c6000 r2 : 00000001 r1 : 00000000 r0 : 00000010
[ 107.108707] Flags: nzcv IRQs off FIQs on Mode SVC_32 ISA ARM Segment kernel
[ 107.121755] Control: 00c5387d Table: 14cb8008 DAC: 00000015
[ 107.133080] Process usb-storage (pid: 1174, stack limit = 0xd59c6188)
[ 107.145135] Stack: (0xd59c7d18 to 0xd59c8000)
[ 107.155073] 7d00: d59c7d3c 60000013
[ 107.168780] 7d20: 00000000 d9966c00 d58abc60 d58abc68 d59c7d64 d59c7d40 c042fa3c c0437124
[ 107.182432] 7d40: c0408ac0 60000013 d5887570 d59b3800 d5835f88 d59b3800 d59c7d7c d59c7d68
[ 107.196117] 7d60: c04330f8 c042f99c c04330d0 d5887570 d59c7d8c d59c7d80 c0408828 c04330dc
[ 107.209858] 7d80: d59c7da4 d59c7d90 c040b250 c0408808 00000030 00000001 d59c7dcc d59c7da8
[ 107.223693] 7da0: c040b2a4 c040b1c4 d5890e00 d59b3800 d5890e00 d5835f88 00000004 d5890800
[ 107.237570] 7dc0: d59c7e54 d59c7dd0 c0402abc c040b264 00000001 00000000 00000000 00000000
[ 107.251507] 7de0: 00001388 d59c7de0 d99af200 d5890e00 d594ea00 0000000d d59b3940 00000000
[ 107.265506] 7e00: d99afaf4 d99af200 00000000 00000000 00000012 01123500 00000200 14cd4000
[ 107.279575] 7e20: 0300125c 01020301 c03ff7a4 d9cf22f0 d9cf22f0 00000012 00000003 00000006
[ 107.293718] 7e40: 0000000c 00000000 d59c7e6c d59c7e58 c0440a20 c0402464 d9cf22f0 d5982600
[ 107.307962] 7e60: d59c7f04 d59c7e70 c0440ce0 c04409c8 00000012 d59c7e80 c0048fe8 00000000
[ 107.322215] 7e80: ffffffff d5a55280 da8d9b80 00000000 00000002 0001e000 c059000a daacd7e0
[ 107.336468] 7ea0: d726d600 0000001d 0000001d 0001e000 0001e000 00000000 00000003 00000012
[ 107.350755] 7ec0: 00000000 00000000 daf1780e 00000a80 00000012 00000000 00100100 d9cf22f0
[ 107.365061] 7ee0: d59c6000 d9cf23a8 00000000 ffffff80 00000000 00000000 d59c7f14 d59c7f08
[ 107.379341] 7f00: c043f6c0 c0440a3c d59c7f64 d59c7f18 c0442058 c043f6b4 60000013 a0000013
[ 107.393598] 7f20: d59c7f3c d59c7f30 d59c6000 d58b0be0 d9cf22f0 c0441e5c 00000000 00000000
[ 107.407866] 7f40: d59c7f64 00000000 d58b0be0 d9cf22f0 c0441e5c 00000000 d59c7fac d59c7f68
[ 107.422117] 7f60: c0041c9c c0441e68 d59c7f94 00000000 c0048fe8 d9cf22f0 00000000 d59c7f7c
[ 107.436411] 7f80: d59c7f7c 00000000 d59c7f88 d59c7f88 d58b0be0 c0041bc0 00000000 00000000
[ 107.450670] 7fa0: 00000000 d59c7fb0 c000fa78 c0041bcc 00000000 00000000 00000000 00000000
[ 107.464883] 7fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[ 107.479035] 7fe0: 00000000 00000000 00000000 00000000 00000013 00000000 1bffa821 1bffac21
[ 107.493188] [<c0437150>] (dwc_otg_hcd_qh_free) from [<c042fa3c>] (dwc_otg_hcd_endpoint_disable+0xac/0xc0)
[ 107.508780] [<c042fa3c>] (dwc_otg_hcd_endpoint_disable) from [<c04330f8>] (endpoint_disable+0x28/0x34)
[ 107.524191] [<c04330f8>] (endpoint_disable) from [<c0408828>] (usb_hcd_disable_endpoint+0x2c/0x30)
[ 107.539346] [<c0408828>] (usb_hcd_disable_endpoint) from [<c040b250>] (usb_disable_endpoint+0x98/0xa0)
[ 107.554955] [<c040b250>] (usb_disable_endpoint) from [<c040b2a4>] (usb_disable_interface+0x4c/0x64)
[ 107.570392] [<c040b2a4>] (usb_disable_interface) from [<c0402abc>] (usb_reset_device+0x664/0x7e0)
[ 107.585673] [<c0402abc>] (usb_reset_device) from [<c0440a20>] (usb_stor_port_reset+0x64/0x74)
[ 107.600646] [<c0440a20>] (usb_stor_port_reset) from [<c0440ce0>] (usb_stor_invoke_transport+0x2b0/0x5b8)
[ 107.616640] [<c0440ce0>] (usb_stor_invoke_transport) from [<c043f6c0>] (usb_stor_transparent_scsi_command+0x18/0x1c)
[ 107.633728] [<c043f6c0>] (usb_stor_transparent_scsi_command) from [<c0442058>] (usb_stor_control_thread+0x1fc/0x2f0)
[ 107.650838] [<c0442058>] (usb_stor_control_thread) from [<c0041c9c>] (kthread+0xdc/0xf8)
[ 107.665475] [<c0041c9c>] (kthread) from [<c000fa78>] (ret_from_fork+0x14/0x3c)
[ 107.679169] Code: e24b1020 eb0019fb e5b51008 e1510005 (e5914020)
[ 107.691750] ---[ end trace d9bbadd0257550e1 ]---
[ 107.702784] note: usb-storage[1174] exited with preempt_count 1
[EDIT]: Added code tags. Rich