Andrew R Stewart 

One thing frame builders have to sometimes do is explain why the customer's wants might not be able to be done. But shop mechanics do much the same too and likely more often.

When I was young a mentor of mine told me that if I wanted to go faster I had to pedal faster. The human body can produce more power as the cadence goes up, to a point. This point is not finite and can be changed with some training or motivation. A different mentor (and at that time future boss) told me to choose one gear easier that I thought was right. This small instruction has resulted in my being what we call "a spinner", cadence on level ground generally between 85 and 100 rpm and higher rpm's when the going get hard.

Pushing a bit of math I find that an 11/70 combo, when riding at 25mph, would result in a cadence of about 50 rpm.(given a 700c wheel). In my world I would be in my 14/44 combo and turning about 100 rpm's. Andy