Are they going to be even faster than the G5's?

You'll need to wait another week until the Universal version of FCP is released. Until then, nobody can really answer that question. However I don't think anybody expects the current models to be faster than the dual or quad G5's from what I've read. But I suppose it will depend on whether they can optimize something in FCP such that it performs better on Intel.

What format of HD?

There are dozens...

720p from a JVD GR-HD1

I also want to use after effects- but I would probably do it by using boot camp, and on windows-