I'm currently stuck in retro-build hell. I've tried two different motherboards and both were DOA, unbelievably.  SO I figure my best bet is to buy an un-opened, brand new board, and i came across a new A7V266-E.

The A7V266-E comes with an AGP Pro slot which should support 3.3v AGP cards, and I've come across a few forum posts where people have said they used the V5 with it, but the manual and reviews say that only 1.5v 4x cards work with it.  Can anyone confirm or deny whether I'd be able to use this board?

It should work - manual really says "AGP pro slot - 1.5 V only" but people run their V5, V4 and V3 cards with no problems in it. On some a7v333 motherboards V5 also runs without problems. I bought few days ago on ebay one a7v266-e rev.2 for my retro 3dfx PC but i do not have time now to test these days. I will post here after testing.

regards

So, I tried my mobo A7V266-C rev 2 with V3 2000,3000 and V5 and it works like a charm although manual says "1.5 V cards only" - it is universal AGP slot on all KT266A from ASUS and on most of KT333 (A7V333).