OMG is all i can say...this is one of those threads like that...
OK
FIRST OFF
the best existing PCI grpahics card is the GeForce FX 5700LE for PCIE
it is comparable to the Radeon 9550
found here:
http://www.newegg.com/app/ViewProductDesc.asp?description=14-140-041&depa=1
that will kill 5200's, 9200's, 5500's, 9250's
it's just better (but some 9200's and 9250's are more expensive as they offer VIVO/better software packages/are just overpriced)
SECOND
PCIe maxes out at PCIE 32x, meaning 32 channels, nVidia's use of PCIE x8 x2 is sort of sad, as it gives each card in SLI a bandwidth of PCIE x8, which is the same as AGP 8x (this is on SLI systems only, on normal PCIE x16 nVidia cards they use all 16 channels)
also, please, please, PLEASE do not put the X600 and the 6800 comparative
it's like comparing a Pontiac Montana to a Porsche 996 Turbo, it just shouldn't be done
to give a list of how the current generation cards, top to bottom, top is best
GeForce 6800U EE SLI($2000 for just vid cards, only from Asus)
GeForce 6800U SLI
GeForce 6800GT SLI
GeForce 6800 SLI
Radeon X850XT PE
Radeon X800XT PE
GeForce 6600GT SLI
Radeon X800XT
GeForce 6800U
Radeon X800XL
GeForce 6800GT
GeForce 6800
GeForce 6600GT
Radeon X700XT
Radeon X700Pro
GeForce 6600
Radeon X600XT
GeForce 6200
Radeon X600
Radeon X300
GeForce PCX 5900
GeForce PCX 5750
GeForce PCX 5300
this is mostly based on THG's VGA Charts V, the 3Dmark05 benching
I added in a few from personal knowledge (they ommited plain 6800's, and the PCX 5300, and the 6800U EE, probably because they are so rare (the U EE))
basically the X700XT and 6600GT are matched
the X600XT and 6600nU are matched
the 6200 and X600Pro are matched
the 6800 and X800 are matched
the 6800U and X800XL are matched
the 6800GT has no place
and the X800XT and above from ATI are the fastest single cards out
and SLI kills all
please
don't use an X600 and 6800 together as a comparison
it's low end to high end
if your buying a new PCIE card I suggest the GeForce 6800GT, as it's well rounded, and offers FP32/PS3.0
which the X800XL does not (sadly, because the X800XL is such a great card that aside)
none of ATi's Radeon X cards offer FP32 or PS3.0
what does this do you might ask?
it means that Radeon X will not be able to play the U3 (Unreal 3) engine to full capacity
which includes A LOT OF GAMES
not just Unreal 3 and UT2k6
Unreal2 has over 100 titles built on it (that were sold) plus countless titles made by average users/at home builders (people who just make games or just levels/scinarios in the U2 engine)