I also have to ask where all this assembly code is coming from, that has to be compiled fast. If it's compiler output, maybe you could hack the compiler back end to generate tokenized assembly code, eliminating a lot of scanning and stuff. It would still be human readable through a simple program that converted the tokens back to mnemonics. The tokens could be 4 digit hex numbers or something like that, so it would still be an easily handled text file.

Lots of simple compilers generate object code directly instead of assembly code, so the above is not so bad by comparison.