Ratings of elite players are inflated indeed. The main reason for it is that pre-elite guys have to face opponents in Swiss tournaments who are performing better than usually (e.g. a 2700 GM gets to play against a 2500 who is performing at 2700 in this event). On the contrary, in elite round robins the situation is more balanced, one gets to play against some people who perform relatively poorly, and some who are doing well.
That's why it's so hard to make it to the top.
Interesting.
Kramnik alternates between being a Super GM and someone who doesn't like the game of chess. Topalov is streaky like Ivanchuk. Carlsen made Vallejo Pons look like a 2200 and then played like Tony Miles vs Adams...
It is tough to tell, I tend to watch Ivanchuk, Shirov, and Nakamura more as they tend to appear in both elite and non elite tournaments. I think how they perform shows roughly what an accurate rating is.