No one can doubt that GSP is one of the greatest pound-for-pound fighters in MMA. In particular, he is a brilliant strategist. How many people do you know who can beat a guy like Josh Koscheck with only a jab? Nonetheless, I think that the probable superfight between him and Anderson Silva is the UFC version of Mayweather vs. Cotto: the best fight that nobody really cares about.
In boxing, everyone wants to see Mayweather vs. Pacquaio. Likewise, in the UFC, the fight that everyone wants to see is Anderson Silva vs. Jon Jones. Granted, Jones is still taking heat after wimping out of a fight against Chael Sonnen. Nonetheless, he remains the most dangerous MMA fighter alive other than Anderson Silva, and is probably the only guy who has the raw athleticism that it takes to defeat "the Spider." I would definitely watch a GSP vs. Silva fight. However, I personally feel that it would end the same way as Mayweather vs. Cotto. In that fight, Mayweather was challenged for the first half of the bout, but then he blew past Cotto to get the decision. Silva would probably do the same thing to GSP.
At any rate, GSP has yet to make his return, which will be in an undisputed welterweight title match against interim champion Carlos Condit at UFC 154. Depending upon how well he does against "The Natural Born Killer", I may have to rethink my prediction in what will happen if and when GSP and Silva finally clash.