Hey, can't wait to see what you end up with, but it really depends on what your looking for. The 2.7t is the best for tuning, stock 250hp, but with chip, exhaust, and a few other mods can get it up to the 330hp. Then you can upgrade the turbos to Ko4's (STAGE III) and get about 450hp. Thats only about 40hp less than a V-8 ferrari F430, but cost about 1/3 the price... On 100octane race fuel you will get over 500hp! The 2.7t is a little less reliable than the 3.0 however. The 3.0 is nice, but if you don't mind paying a little *maybe alot* more on repairs then the 2.7t is the way to go.
However consider the 4.2, not too sure about repairs and reliablility, but the car has wider wheel flares and door blades. The 4.2 is by far the best looking of the 4 engines availible in the
a6 model