ATI reference Catalyst software will work fine on ASUS cards, but you will lose ASUS specific tweaks, like their version of temperature monitoring, etc. Temperature monitoring is available using the latest Catalysts, but there are other little tweks you may like (don't know them exactly) Stuff like VIVO support may be ASUS driver related.
As for the R9600XT versus the R9800. I would recommend an R9800 once the new cards hit the market. Likely to be a good price drop on them. Otherwise go with an R9600PRO for best bang for buck, by then they should be around the $100US level.
You will likely enjoy the experience of the R9800 more, so if you can afford one definitely get one. But the R9600Pro has undeniable peerformance to price advanatages especially when up against your average overpriced XT. At the same price of course the XT should give you more for your money 9 times out of ten.
So wait for about 2 months and the prices should drop like a stone on pricier R9800s (PROs XTs), and even drop a bit on the R9600PROs.
- You need a licence to buy a gun, but they'll sell anyone a stamp <i>(or internet account)</i> ! - <font color=green>RED </font color=green> <font color=red> GREEN</font color=red> GA to SK