with the combined power of the most powerful wepon in the universe that has unlimited power and the most powerful wepon in the anti matter universe that protects sinestro from harm like hals did it could happen i mean if they dont try and kill eachother
When the rings are used together in close proximity, it increases the power output. Speed, power, durability etc. Thy two(if fighting together) would feed off each other thus amplifying their powers.
While I think it would be close and the duo would take a good number of matches, Thanos is such a tough bastard that I have to think he'd take the majority. I mean there aren't too many beings who can shrug off blasts from the Silver Surfer like they were nothing. http://img75.imageshack.us/my.php?image=surf0na.jpg
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