The 2.60C-2.80Cs can be pretty obstinate and while they can do 3.3 gig at below default voltage, they hit a wall fast and won't budge.
As for your 285, 5:4, 2-2-2-5, try benching 3D
. Not just on the Epox, but almost every other board I've tried ('cept the Asus) you can be 2D and even SuperPI stable over 280 at 5:4, but 3DMark2001 will kick out or reboot the computer. All you can do is drop the fsb until both 3DMarks pass, and throw a lot of other 3D at it, particularly the SS2nd Encounter and IL-2 Sturmovik demo loop. I have passed all three 3DMarks but you may encounter SS dumping to the menu screen or get an error box halt IL-2. That or just plain lockups. IL-2 tends to reboot the computer when running or exiting.
Also, on the KHX3000 (BH-5) I tried on the 4PCA3+, it would not pass 3DMark2001 at 5:4 above 265 fsb, even though it did DDR490, 2-2-2-5 at 3.3 volts at 1:1. Figure that one out. The SD/CW boards runs best at 1:1, then 3:2, then 5:4.
I have three 2.40Cs that max out at 287-288 on other boards. I can only run them up to 279, 5:4, 2-2-2-5 on the 4PCA3+.