I recently replaced my IP5000 40C packs for some Vampire 6200 60C
honestly, I dont notice the different in punch or top end with a 13.5 boosted.
The only thing I noticed is that my car still feels punchy for the full 5 minutes, my my 5000 40C, even though I was only pulling 2000mah the packs started to feel less punchy for the last 3 laps (of a 21 lap race). not much, but just a tiny bit, maybe not even a tenths worth.
But the new packs stay cooler over the run - dont know if that is better or worse, but the older ones got to about 36 degrees, the new ones get to 31 degrees (on a warm UK day).