FWIW, I was curious about it. I plugged all the values into Sheldon Brown's gear calculator. Given a wheel size of 700x32, a crank length of 170mm, 40/20, 50/25, and 30/15 front/rear gears work out the same as in gear inches and gain ratios (which takes into account crank length).

54 gear inches and gain ratio of 4.0 for all three combinations.

Unless there's some other factor I or Sheldon overlooked, I can't see how they'd feel different.