Other than higher core/memory speeds there is not much new under the sun, except the new 'Overdrive' function which can be enabled in the Catalyst drivers :
ATI have taken a different approach here, and by virtue of an on package thermal sensor for Radeon 9800 XT and on chip sensor for 9600 XT, if Overdrive is enabled the core speeds will gradually increase until such a point that the meet a specified heat output and then the speed will be scaled back down slightly to remain under that limit. While the core speed will never drop below its preset speed, should Overdrive be enabled you can then gain extra performance from the board should your PC case environment be suitable to do so.Here is a snip from the review over at HotHardware :
Physically, the Radeon 9800 XT is easily the nicest looking piece of graphics hardware we've seen in the HotHardware labs in a long time. Best in class performance, great image quality and killer good looks, is a powerful combination that is hard to resist. Once again however, you've got to pay to play. The Radeon 9800 XT also retails for $499. We expect to see street prices well below that range eventually but once you get into the $400+ territory for a Consumer 3D Graphics solution, it's obvious that the product is clearly targeted exclusively toward the high end niche´ enthusiast end user. From a price / performance perspective, the real sweet spot in ATi's product line-up, will be either the Radeon 9800 Pro 128MB cards or the upcoming impressive looking Radeon 9600 XT. By all rights, Radeon 9800 Pro prices should drop like a rock, once this new high end card gets out on the street. So keep an eye out for deals on R9800 Pros.