The Serpent Rider wrote:Anything up to GeForce FX 5950 Ultra or Radeon 9800 Pro. But the most powerful card that can work with AGP 3.3.v Slot 1 system is Galaxy GeForce 7950GT.
Of course you could go for a Slot 1 system with AGP 4x, allowing lower voltage options. You could do that with either an Intel i815 chipset (slot 1 i815 was very rare, but IIRC Abit had at least one board), for highest performance, but the usual i815 limitations (512MB RAM...), or the slightly slower but far more versatile Via ApolloPro 133A (694X) chipset.
Abit's SH-6 would be the obvious i815 choice, for Via 694X there's much more choice, things like the Asus P3V4X, Abit VT6X4 or Soltek SL-67KV. Iirc the Asus board offered the best (non-overclocked) performance.
A P3V4X with Tualatin slotket and Radeon 9800Pro would easily beat any BX with the same CPU and a 7950GT, assuming at least that the CPU wouldn't be the bottleneck in both cases.