What would the difference be? Other than rotational inertia, the only difference I can imagine is that the 700C wheels will put fewer RPM on the bearings, and thus possibly less total friction. But that would only be noticeable for really crappy wheels.

The larger questoin is what you want the bike to do. Are mountain bikes 'zippier'? Perhaps because of the smaller frames they feel more nimble, and they probably can accelerate pretty well. I wouldn't want to ride long distances on a mountain bike, though. Maybe an old-school touring bike would suit you well?