APR is a safe bet. GIAC's good to know, more brutal seems more powerful but also more strain on turbos. More boost I think.
VAST makes one that is real powerful but don't know much about it

 

I would have to go with Kevin and Slurm. The turbos are alot to maintain though and its always in the back of your mind. I still love it though . Both great cars.

 

What a debate the score is tied 9-9. IMO I like the look of the 4.2 better and also in theory more reliable, but that can depend alot on the cars history when dealing with 5-8 year old cars. Who knows how hard they were drivenor how well they were kept up.I bought a 2.7t a couple months ago, 97,000. They guy I bought it from was the only owner and had an extended warranty and had it regularly maintainedat an audi dealership. I was lucky enough to get all the receipts of everything that was ever fixed on the car inculding the whole timing belt package and the cluster at 85,000. Knowing that the car was taken care of in this way makes me feel very confident that it will be very reliable for years to come. As to my vote I chose 2.7t because the deciding factor is transmission, MANUAL. Them bums at audi forgot to make the 4.2 a manual and thats all I'll drive.

 

please read around as you will see there are a number of people here who are working with VAST to take on and test their 4.2 mods with stunning success. the "no Mods" argument is changing weekly. by stage III, the 4.2 is an incredible beast. I know mods aren't your thing for this particular discussion, but that has been much of a point made here and I just want to make sure you are aware that they are now being made and with great success for the 4.2. I am considering them myself.