I am 5' 1" and I have had bikes with both 650 and 700 wheels. There is not a major difference in speed! The only reason I noticed a slight increase in my speed when I went from the 650s to 700s was a decrease in the weight of the bike and an increase in my ability! I had no toe overlap with either of them. If the bike is fit correctly, it won't happen. These 2 bikes were very different sizes and they both fit me. Differences in other parts of the geometry account for this.