I'm a lightweight too. Many years ago I rode on 27 x 3/4 " tires and apart from the gee whiz effect of such small tires I can't say that they provided ANY benefit at all. My experience was that they were very rough riding with less grip.

Apart from a small aerodynamic advantage to the smaller tires the larger tires have the benefit performance wise with better grip and less rolling resistance so why don't you like the proRace 25's?

I'm running 650 x 23c at the moment at quite LOW tire pressures. I run 75 psi front and 85 psi rear. I just don't need any more than that and higher pressures just mean a bumpier ride and more skitish handling.

Regards, Anthony