Um, best episode ever! I was certain that Nate and Jen would end up winning the whole thing, so to see them eliminated was a huge relief. I don't think I've ever been happier about an elimination.
For the first time, I'd actually be content with any of the final three teams winning, though I'm really rooting for TK and Rachel. They've managed to stay likable and level-headed throughout the race. I want Ron and Chris to win the least (simply because Ron still seems like a huge jerk, even though his attitude has improved), but I won't be upset if they win.
If I had to make a prediction, I'd say Ron and Chris will win. Like you said, Jen, there might be too many physical activities for Don (and Nick, really -- he doesn't seem very athletic). And TK and Rachel tend to make small errors, so that might hurt them in the final leg since there's no room for mistakes.