I'm curious if it's possible to change the multiplier via a custom BIOS to run say a 1GHz upgraded Xbox at ~733MHz (for the best compatibility). At first, I imagine it's not possible since the original CPU was never clocked up/down via a BIOS hack from my knowledge, but maybe it was the CPU that was the limiting factor and not the Xbox itself back then?
No, theres no way to overclock or underclock the original xbox via software. The way Trusty does it is actually by lowering the voltage to the 1.4ghz processor to make it run close to the original 733mhz to try to fix the game issues. Doesn't work perfectly though.
Based on this page, it sounds like it's via clock divider: http://www.xbmc4xbox.org.uk/forum/viewtopic.php?f=13&t=2454
