I'd stay away from the X1600... too many weird benchmark showings. Drivers aren't quite solid yet, IMHO.
For under $150 the X800 GTO 128mb is the best bet by far.
If you're hitting about $200 the 6800 GS and X800 XL are both good buys. the X800 XL is better stock, and the 6800 GS is a better choice for an overclocker.
But if video encoding is a bigger priority than gaming for you, the 1600 wouldnt be a bad choice too.