I put 81,000 miles on an '01 996 tt with an Upsolute chip (Upsolute.com). It had 510 hp, 487 ft/lb, and would beat about anything on the road. Awesome, awesome car. You don't need the X-50, but it is nice. The larger turbos don't spool as fast, but have a 600+ HP output. There are also hybrid turbos and Garrett ball bearings for those with even more taste for speed. The tranny seemed fine to me for all of those miles, and I drove it HARD. The car was hard to launch, but tracked very well in most weather conditions, tires permitting.
IMHO these cars are amazing. I have a 335 i now due to the high cost of operating the Porsche, but I will return to Porsche in the future, cost permitting.