I've got some similar fit problems to those here, although I'm 5'3" and ride a 51 time trial, so not really a teeny frame. I tried 650 wheels before I bought my bike (on 700s) and I didn't find much difference in practice in climb and acceleration; certainly not enough to make up for losses downhill and on the flat. One thing's for sure; don't put 650 wheels on aframe built for 700s. Nothing will work. Also, there's less choice in wheels and tyres for 650, and if you get into trouble on a ride or at a race it's harder to borrow kit. Try to borrow one first, before you commit.
I have a bit of toe overlap (I also have big feet) and I ride 170 cranks (I actually fit 167.50 but those are hard to find). Out on the road though, it's never been a problem, but maybe I just haven't turned sharp enough (although if you're turning that sharp you probably shouldn't be leading with you're outside leg anyway, for balance). best thing is to get a professional bike fit and then try to get your bike to match it as best you can. Custom bikes sound great, but I've heard of ther examples where frames didn't work so well (including a time trial bike where the rear wheel actually rubbed the seat tube because the cutaway was in the wrong place!)
Good luck!
