Performance
Four of the latest games are used to guage the GeForce 6800 GS's performance relative to the other products.Quake 4
The GS is slightly behind the GT it replaces, but lies comfortably ahead of the ATI Radeon X1600 XT by nearly 30%. All boards are at least ~40% shy of GeForce 7800 GT, showing what the next step up the ladder from those three products is.
Call of Duty 2
The same overall trend is visible in CoD2, just the relative gaps in performances between the products are different. X1600 XT doesn't trail by as much as it did, although it's still outgunned by a fair margin by 6800 GS and then 6800 GT, with 7800 GT showing all three how it's done these days in a modern, affordable high-end part.
Black and White 2
Black and White 2 is a fairly 'math heavy' game title, relying entirely on the performance of your shader hardware, above texturing performance, in order to run well. X1600 XT looks good because of that, its triplet of pixel shader ALUs, per fragment shader processor, able to let it do great for a part with only 4 fragment units and 4 ROPs.
That said, 6800 GS and 6800 GT best it, with 7800 GT far ahead.
Splinter Cell: Chaos Theory
SCCT shows the same performance trend as seen already, this time with X1600 XT trailing by ~20%, 6800 GT faster than GS by ~5%, and 7800 GT up on top of 6800 GT by over 20%, on average.