I don't know. The only people who might are under embargo. It's certainly possible.
Midnight Club LA was sub-hd, however I could barely tell a difference in the comparison shots, to the point where it would be imperceptible to me in motion.
GTA4 was also sub-hd however to quote the guy who pixel counted it:
http://forum.beyond3d.com/showthread.php?t=46242&page=21
RDR had no lead platform. Each console had its own team. One console may have a small advantage, but nothing "substantial". I'd like to think they learned some things since GTA4 shipped 2 years ago, and then I wouldn't call the differences "substantial", if you didn't read internet forums, you wouldn't know.
I'd like to see a comparison too. If I were betting, logically, I'd say X360 will be judged superior, considering it's what they've showed off. But I tend to think CheapyGamer's comment was FUD.