Remember, half the time riders are showing off. I was on a ride (25 riders) where the first mile was at 26 mph. I was 100 yards behind EVERYONE thinking I should have stayed home in bed.
10 miles down the road only 5 other riders could hold my wheel doing 18 mph!
I've seen it a thousand times!
I say yes, a bike can make a difference but training is the biggest factor. I have 275 lb buddy that makes fajitas out of some 150 lb roadies.