Like what I said earlier, the 20incher will be quicker from a stop and go, but the 700c could be faster in the long run or at least more comfortable to maintain the same speed. Then again, it would really depend on components like the drivetrain and tires/wheelset. I went on a bike ride with a hybrid,fixie and a roadie when I was on my Dahon Speed P8 (upgraded to a double crankset older ultegra ~2005) and I got to drop them on a climb in a bridge but on the way back I kinda kept up with them but was struggling to do so. On the flats in the greenway/trail, roadies seem to just zoom by me, of course those are fitter riders and on a lighter/faster road bike set-up. A 53t by 11t geared foldie would be slower to a 53t by 11t geared 700c given the same cadence/effort because of the smaller wheels I think.