He plays just fine on clay, its funny a lot of people forget how good he was at that French Open. In my opinion I thought his level of play was every bit as high or perhaps higher then it was even at the US open, he had been great all tournament and he outplayed Federer most of that match, but his major mistake was that terrible second set tie break that cost him that match. It took me a good month to get over that loss because I still believe he was the best player at the French open that year and had a golden opportunity to win it.
His endurance at that time wasn't good enough, he had a decent chance of taking Fed out and probably would have won.
That year he also made the final of the WTF.
Very close of having a couple of slams and a WTF title for the year.
At those times he was improving by the month through the whole year.
I don't believe he ever reached his peak, there were areas he could definitely improve even then.
Hard to tell where he'd be now if not for the wrist.
He has a better chance of beating Nadal at the french than Federer IMO. Just a better matchup.
We'll see how he does this year but he may not have his game back by the french to challenge the best.
I expect him to be better than he ever was, he's older, stronger, getting more experience and there's areas he can improve.