I love our GP 3300's. We bought 10 or so and torture them every weekend. They have been bruised and batteret but still work like a champ. We should probably look into re-zapping and re-matching them, but that's after the season is over.
I can not tell you anything about the 38's as I have never raced them, but what I can tell you is that I beilieve that they have slightly higher internal resistance.
I am not sure about how much punch they will have, but at 1.90-1.94 I think they will definatly outpunch most everyday GP3700's no problem. The price on those 38's is outstanding! I don't think I have seen a better deal for such voltage before.
I would say go with what gives better punch. In this case it looks like the 38's are the best way to go, but we have had tremendous success with our GP cells. We were running some older batteries. The best of which being a 3000 pack. After the season closed and I built my new Bandit
we decided to go with some new batteries. We bought 10 matched packs and wired them up right. The voltages were average to above average, and the runtime was great. The first official day of racing my new Bandit won 7 out of 8 Pro-Stock Stampede races. I used a new speed control, a new radio, new internal components and new aluminum, but I took the motor out of the car I was racing. The car with the new GP33's flew!
Normally, I would say go for the GP's, but in this case looks like the 38's are the way to go. That voltage is absolutly insane and that price is just unbeilievable.