I just put a pair of 2" Schwalbe Kojaks on my old Trek 930 and am really pleased with them. The ride is so much smoother and quieter now, and the new tires grip the pavement noticeably better than the old knobbies. Plus they're a bit zippier and it's easier to pedal up hills. I've been riding them at 70 psi and the only downside so far is a slight bit of extra harshness over the biggest bumps, but I hardly notice and the benefits are so worth it.