Here are two GTX BIOS revs to try for anyone interested.
KO-Rev3 - based on a newer BIOS build, this BIOS uses a 50 Mhz delta as well as a better blended 3D throttle (432 with 40 delta). The default clock is 490/1200.
KO-Rev4 - same as above with 500/1350 as default clock. This is the one I use.