Jerryz, of course the hams aren't as strong as the quads (I think in some powerlifters hamstring strength of 80% of that of the quadriceps has been observed, usually the hams are 1/2 as strong if you grab a guy off the street), but I can tell you I'm pulling up with the hams and using the hip flexors too when attempting a maximum sprint. When doing steady state endurance cycling, I don't feel my hamstrings and I don't attempt to pull up but just move my legs out of the way, as you say.
Quite frankly, stronger hamstrings are considered a benefit for 50/60/100 m dash, and the running motion is quite similar to cycling, if anything the smaller movement circle (partial range of contraction of muscles) and lower leg velocity allows for generation of even higher forces (for duration, not peak) during an all out cycle sprint, so I would expect strengthening of hip flexors/hams to be of benefit to a sprint cyclist. Regular back squats will strengthen both, along with the quads and glutes.
As to how much I've lifted in the gym, for a max leg curl, probably about 85 kg. I've trained squats and deadlifts for years maxxing at about 240 kg DL, although I'm much weaker now as big back muscles aren't useful for endurance cycling.
-Bikeguy