Lapentti seems to me like a physically fit guy. I remember him having a number of gruelling matches back to back during the clay season and he didn't really seem affected then, but I suppose he is getting on a bit now and hard courts are more punishing on the body.
Lapentti seems to play in the most energy-conserving way possible...doesn't get excited and just plays his game, that's why he often wins long three setters when he has more in the tank at the end. That said the match against Verdasco is hard to call.
Having watched both Soderling and Kohlschreiber this week, there's no doubt that Soderling is playing well but when Kohl played Jun I was surprised how sharp and focused Kohl was, he seemed to play better than you would expect judging from recent results. So I am making the presumption that Kohl upped his game so Soderling is not a bet (maybe a small interest on Kohl).
I like the chances of Karlovic and Tursunov.