I used the IP3800s in modified touring for a few weeks and they had enough power and punch to drive a Speed Passion 3.5. Geared around 12.6:1 on a 80m long very technical carpet track I was using about 2700-2800mAh. On a large outdoor track thats about 250m long, I hit the voltage cutoff about 1/3 way round the victory lap but they did last the 5min run. That was geared around 10.5:1 with the same motor. I had to gear 1 tooth on the pinion smaller than the best ratio for that track due to heat and lipo swelling issues (just heat expansion in the pack, but figured it was safer to drop a tooth on the pinion to stop it).
For stock or even super stock, the 3800 25C pack will be more than adequate. With a 19T brushed a guy I raced with pulled about 3500mAh on the same large outdoor open track (asphalt) and about 2400mAh on the short technical carpet track. With a stock 27T you should be able to run at least 2 races without charging on the 3800s.
I now run LRP 5300 28C Competition Car Line packs and there is no real difference to the punch they provide, but the packs run a hell of a lot cooler in the car when I gear the 3.5T hard on the large outdoor track I referred to.