The 320 will not be a handful with the 330s in it. The velocity doesn't need a lot of trim to get it to run. With a set of labbed B1s that have been worked you can run just over neutral and the boat will fly. My 41 with hydros has to be trimmed to the moon, but with a set of Labbed B1s that have been worked further, with them spinning in, just above neutral is all she needs. One thing I would definately do with a 320 is to put the 30" tabs on the boat. In any kind of slop you'll want the longer tabs.
Velocity is a drivers boat, you'll get the feel of how to keep the boat running on the pad, if you don't you'll never realize the full potential of the boat. But again with the 330s it's pretty much a sit back and let her fly kind of boat.