I don't know much about 650c wheels, but presumably, the gearing on the 650c-wheeled bike will compensate for the difference in tire size. I ride a Bike Friday in addition to my Luna (700c wheels). The Bike Friday has 20" wheels. It goes everywhere and as fast as my Luna (but it also goes in a suitcase, which is nice). So wheel size is not a factor in speed--the rider is.

While your measurements may not require a custom frame, you may still want to look into one given your budget. Nothing is quite like having a bike that fits you.