The main factor that kills the X1600XT is the 128-bit memory, if it had 256-bit memory it would make mince meat of the 6800GS, but unfortunately it does not.
oh i found this
Leadtek NVIDIA GeForce 6800GS 256MB DDR3 PCI-E
there aint much difference with this is there?
XFX GeForce 6800 GS Extreme XXX Edition 256MB
Which is better? BTW THE LEADTEK IS CHEAPER
Ok, here is probably your best deal: http://www.newegg.com/Product/Product.asp?Item=N82E16814130271
A 6800GS for $179, with an instant $10 rebate, and a 15$ mail in rebate on top of that. This brings the price to $154. It is also factory overclocked and the warranty is lifetime and covers overclocking.
EDIT:
You are not in the USA. XFX usually is not that good, I would get the leadtek.