one more difference between the P4B266 and -C is that the -C only has two memory slots. i have right here asus P4B266-C, and an Epox EP-4BDA. they both overclock exactly the same for me. my 1.8A does do around 2.6, with a 146 FSB. i can go higher, but my PSU is crapping out on me, only around 11v on the 12v line. this normally doesn't matter, but the P4 draws power from the 12v.
personally, i like the Epox better, because it has more options, like a 1.85vcore, and higher memory voltage, 2.9v vs. 2.7v on the asus. both are quality boards. antec 400w coming tomorrow, so i should get a higher overclock, especially since my temps are in the low 30's with my watercooling system on it.