I had very little problems running ANY agp Nvidia card on my Asus P5A. One of the few problems was an Asus Geforce2 Ti but an Asus Geforce2 GTS runs fine and so does an Ultra (which is weird). No problems with geforce256, geforce2 (mx), geforce3, geforce4ti and mx.
A lot of cards might however be a bit tough on the agp power supply that is used on some of these old boards. For that reason (and obviously bottlenecks) I would not go higher than a Geforce2. MX is also excellent and has more than enough power for any cpu supported by these boards.
Also tested my Aopen mvp3 board with a lot of cards with almost no issues, same for my gigabyte, DFi and Epox boards. Stop yelling about the issues and start testing.... many boards run fine with most cards. I have A LOT of ss7 boards from different brands and they are not having the problems people keep repeating here for years and years. JUST USE THE RIGHT AGP DRIVER AND BIOS SETTINGS.
Sure some may have more issues but I had my fair share of problems with Athlon setups as well for example (don't get me started on slot A) and even some BX boards.
asus tx97-e, 233mmx, voodoo1, s3 virge ,sb16
asus p5a, k6-3+ @ 550mhz, voodoo2 12mb sli, gf2 gts, awe32
asus p3b-f, p3-700, voodoo3 3500TV agp, awe64
asus tusl2-c, p3-S 1,4ghz, voodoo5 5500, live!
asus a7n8x DL, barton cpu, 6800ultra, Voodoo3 pci, audigy1