Mr Monster Legs and I hit 37mph on the Prospect Park downhill this morning. I'm riding 49x15 and I think He is riding 48x16. My gearing (as some folks who saw me on River Road on Saturday will tell you) makes uphills any steeper than the one in PP a total nightmare. I mashed up the hills coming home from Nyack at 8mph until I cramped my calves.
I think fixed gear gives you a tremendous advantage in traffic where it is all about control and confidence and it gives you an advantage on the flat (if your gear is right) because fixed gear is all about going with what you got and not fussing with the machine, but hills up and down are where you get handicapped for your lifestyle choice! That being said I find that on the hills that don't shut me down I pass roadies all the time... they seem happy to do 100rpm spinning up a hill at 5mph... which I think is odd.