Actually, ColdFire will be _much_ faster if you're running 68K/AGA stuff. Even 1.4GHz G4 emu will be inferior to actual hardware in combination with ColdFire.
One doesn't rule out the other though. Peg/A1 will be much faster running their native stuff. Stuff which some day probably won't appear as 68K versions no more.
Personally, I think I'll buy both (ColdFire & A1). But I'm not going to buy an A1 until OS4 is released. If I hadn't already had RHL on my x86 already it would have been a different matter though.