Thanks for trying, link wasn't useful, web searches useless, i810 graphics so 2001 !
After much time trying everything imaginable (w/out xorg.conf tweaks, intel vs vesa, boot codes, etc) 800x600 with vesa only. Tried upgrading TC6 -> TC7, exact same behaviour. Don't know if dCore's xorg-intel is from TC7 or from Ubuntu repo proper, but same result, only vesa works, extremely poor resolution without xorg.conf, which gets it up to 800x600. Not bad actually if you take the time to adjust toolbar, icon and font sizes but i'm used to 1200x800.
So exact same hardware and xorg.conf file runs dCore-jessie and TC6 perfectly. Maybe approaching end of the road, appears i810 support silently dropped, >15 years is a good run and Jessie gets LTS until 2020. If this hardware is still around and dCore-stretch gets released, will give that a go too. Posted from TC7, 800x600, Dillo. Otherwise TC7 is nice, thank-you to all the volunteers that make it happen.