Yes cycling is against the clock, but the other riders have the same clock.Just like in a 100m dash. you are competeing against the clock... and the other runners.

I think of golf the same way you can go -10 to par one year and win a tourney, yet finish way out of it with the same score another year.

Armstrong (although retired) has clearly dominated his sport for a long time... I think one thing against him is just the time a race can take... I mean, lets face it... watching a Tour de France stage isnt as exciting as watching Michael Johnson run 200 metres in an unbelievable time, is it - even if both are purely physical triumphs?

I think, to me the key is kind of - that what someone like Armstrong does is really based on fitness, strength, heart... while someone like Federer is just graced with such skill. It isnt that Federer has won so many more slams than anyone else (which he hasnt, but probably will if he keeps playing up to 30)... its just the way he seems to be able to reach, consistantly, another level of skill, another level of brilliance.

I genuinely think Federer is capable of moments, with reasonable regularity, that no one else in the sport can even imagine performing. Someone like Armstrong has shown himself again and again to be immensly strong, but its somehow different, at least to me.

If you base it on potential, I would without a doubt say Shaq, but since it results, I vote Lance.
As far as how many Slams Federer wins.. that would be 0 right now.. at least in the all 4 majors at once definition of a slam. If you meant majors won, then you can't extrapolate how many he wins in the future based on his past or present. He could lose his focus/desire, he could die of an anyeurism, he could meet his Yoko... anything could happen.