I have a 128Mb Chaintech 6600 AGP with crappy 4-ns Hynix chips (500MHz DDR), and it seems it doesn't like any other 6600 BIOSes out there (at least none of the ones from MVKTech.net). After a forced flash (using -6 -5 -4), what I get is a garbled text mode, and it only gets worse from there, so I'm pretty much stuck with my stock BIOS.
Any ideas?