i have been using vtec 3700's recently and i can't fault them.
the punch is about the same as my promatch 3300s but they have roughly 30+ secs more runtime than the GP3700s are getting (from what i have heard)...30 secs don't sound like much but it could be a matter of a lap.
also, the voltage seems to be around .2 per cell higher than GP 3700s (GP3700s seem to get around 1.18, where as the vtecs get around 1.2+)