If you're after video card comparisons, check out the "Fastest Graphics Cards of 2004" article on XbitLabs. Part 1 and Part 2 together cover 27 cards.
On the modding side of things, ARP have a Radeon 9800 to FireGL X2 guide posted. TechPowerUp meanwhile cover X800 voltmods, including VGPU, VMem and VDDQ on Pro/XT/PE cards.