700c -> 650c on a Road Bike

[profàvélo]

Toe overlap is a hugely overrated problem. It only occurs when you turn the wheel a significant amount. When actually riding, one turns the wheel very little and uses a shift in weight to take a turn. Shoe size does affect the degree of toe overlap.

I agree with Doc that toe overlap is an overrated (and misunderstood) phenomenon.

The custom fit kit at Seven Cylces has an excellent explanation of toe overlap and how trying to eliminate it completely often means a sacrifice in the bike's handling. I would simply copy it here, but it's a PDF. I highly recommend that you read these few paragraphs (on page 7) before deciding that you must eliminate toe overlap at all costs, because there are probably costs involved.
http://www.sevencycles.com/order/CustomKit2006.pdf