For the TCS race at 180 Raceway I ran the Gens Ace Redline 2.0 6500mah battery and my car was the fastest GT ProSpec there, just not the driver...LOL . I qualified 3rd and was very close to the front two runners but screwed up in the main and fell back. But if you are running GT ProSpec and following the 1400g minimum weight rule then the way to go is a full size pack that gets the car to the minimum 1400g. The bigger packs have lower IR's and much less voltage drop off.

If you don't have a weight limit rule, then run the shorty pack to the rear. Before the implemented the 1400g minimum weight rule by GT ProSpec was under 1200g with the small shorty pack.