I didn't say that no one besides Nadal would give Fed a challenge on clay. I said that no one would give him AS MUCH trouble as Nadal.
Changmaster, I know you know a lot about tennis, because you have played it a lot. I have played a lot of tennis as well and watched it intently since the mid to late 1970's.
Having said that I know I am a Borg "fan". I am also not one to disparage Federer without reason, in any way. He has few "weaknesses" on his resume, as is true of other guys at the "summit" of Tennis (Laver, Borg, Sampras, and Federer in my opinion).
Yet, I guess we'll have to agree to disagree here. We just have different opinions, that's all. Very few things in Tennis are "set in stone", especially when all time Greats face off and play each other. Of course, as to how Federer would have done against past greats on Clay is purely hypothetical.
You say that "few would trouble him as much as Nadal", but I would disagree with that. I've watched all these players play in their prime at the French Open and also Federer. I'm not contending that Federer is not a great clay courter. He is, and has impressive results at the French, but there just is not the same level of "clay court expertise" now as there was in the past. A big reason for that is that so much of the Tour is now devoted to hard court tennis, with less emphasis on clay, but of course the French Open is still a big Slam. There are not very many "clay court specialists" around these days. In the late 1970's you had Dibbs, Solomon, Orantes, and the list goes on. They LIVED to play on Clay primarily. They would dig their heels in and dare you to beat them and with wood racquets, believe me, it was not easy to beat clay masters. Yet, on clay, Borg had it all, power, finesse, speed, quickness, stamina, patience, resolve, mental toughness, and even sliding ability. He skipped the 1977 FO, and lost to Panatta once when he was "of age", but besides that he was untouched from 1974-1981. He took on all comers and retired as clearly the best clay courter in the World. Wilander won in 1982 (5 sets over Vilas), was practicing with Borg that year and said "he couldn't win a set against him".
All the following players, in my opinion, would give Federer "lots of trouble" and several would more often than not beat Federer on clay (especially Borg and Lendl) but I know you disagree with that:
Rosewall, Laver, Borg, G. Vilas, Clerc, Wilander, Lendl, Courier (his best years), S. Bruguera, Kuerten, Muster, and Nadal.
(This is assuming that the players were using the same equipment, with both playing with wood frames or both with modern technology (latest frames, with Luxilon/Gut, in hypo matches at RG)
Here's an example (Wilander vs. Lendl 1985 FO,
http://www.youtube.com/watch?v=yGvW40l43e0, and 1987 FO,
http://www.youtube.com/watch?v=ZxmgflWQsUg)
How? As I've mentioned before, all these guys were amazingly consistent AND they would not easily be overpowered by Federer either. Plus, they all have great stamina, but I'm not saying that Federer is not a great athlete as well, he is. All the guys above, except for perhaps Laver, LOVED to beat guys on clay. They thrived on it and relished it. They would make opponents suffer greatly, and had all the skills to back up such an approach. I know Federer would try and hit lots of service and forehand winners, but I think most of the guys above would eventually break down the Federer backhand over the course of matches on Red Clay. Eventually, I think that would outweigh Federer's ability to hit forehand winners to somewhat compensate for that.
Anyway, I know you disagree with that, which is fine, you have a different opinion, and it is an educated opinion, that's not just a guess or feeling. I don't think you are trying to "take shots at Borg" either. I'll put Federer much higher on the "clay list" if he wins another RG title, especially if he either beats Nadal or if Nadal does not perform as well as he does at RG this year.
If Federer beats another 7 guys and takes FO title #2 that will really speak to his versatility (like holding serve after breaking). As of now, even if Nadal does not win the FO, I do not see Federer as a lock. Del Potro is also a big threat there if healthy (he's one year wiser and more "grizzled" which will serve him well the next time he plays Federer). I do think that his chances of winning at the FO this year are much better than they are for Murray, Davydenko, or Djokovic even. It should be a great tourney.