650c wheels are not necessarily slower. Some think, you can get a faster acceleration on 650c than you would with 700. Personally, I prefer the 650c wheels. I felt more in control maybe it was the total bike thingy.

Drawback is the obvious limitation to availability of wheels. I wanted Accent wheels sometime ago but they were made only in 700c size. Tire selection and tube selection isn't too bad if you go on line.

My current Obera uses 700c wheels and it took maybe 30 minutes of riding to get used to the new wheel size (maybe it was the total bike again).

Go with what makes you more comfortable.

Now on a smaller frame, 650 vs 700 will make a difference in the geometry. You don't want too short of steer tube. 10 to 12cm is the absolute minimum you want to go. Anything less and I think your head set will wear out much quicker... And for this reason alone, you may want a 650c wheels. It allows you to have longer steer tube.

shawn