Toasted my old Ti4600 card this week, the fan finally went out on it and I can't manage to get the old cooler off without destroying the card. So I picked up a new GeForce 6800 for $300 (which was the next reasonable step up from the FX 5900 XT).

NVIDIA GeForce Ti 4600
NVIDIA 61.77 (stock, high performance, 128MB aperture)
A7N8X-Deluxe motherboard AthlonXP 2600+ CPU PC2700 DDR
AquaMark3 Score: 19480 (CPU: 6286, GFX: 2304)

GeForce FX 5900 XT
NVIDIA 61.77 (stock, high performance, 128MB aperture)
Asus SK8V Opteron 144 PC2100 1GB
AquaMark3 Score: 36520 (CPU: 7260, GFX: 4878)

GeForce 6800
NVIDIA 61.77 (stock, high performance, 128MB aperture)
Asus SK8V Opteron 144 PC2100 1GB
AquaMark3 Score: 46982 (CPU: 7008, GFX: 7122)

So, it's about 28%-45% faster then my old FX 5900 XT card. Not a bad bump in speed, and a good deal faster then the old Ti 4600 card. Top scores for NVIDIA cards are in the 55000-60000 range, so it's not that bad of a score.