Basically these are the optimizations: i686 build with -O3 optimization, eliminated urlclassifier altogether, set default cache to 20MB, reduced maximum default popups. The mozconfig file in the source directory lists the configure options for compiling.
I think that the difference in speed, memory usage, and such can be measured in a few percentage points between the official Firefox and a custom build. Either way you slice it or dice it, it is still Firefox and is resource intensive. Even the 2.0.0.20 build consumes almost the same memory as the current. Of course, correct me if anyone has some benchmarks that tell otherwise. But hopefully by at least eliminating the urlclassifier and trimming down default cache it will be more freindly for TC users, especially those that run with /home in RAM and back it up on shutdown.