[IMO] Luke Thomas broke this match-up down the best way it could possibly be broke down.
It's pretty long so if you have the time, it's well worth the watch.
If not, basically he explains that as far as negotiating goes, GSP is in a tricky spot when it comes to fighting Anderson Silva. The closer to 185 this fight happens, the more advantageous it is to Silva. But if Silva were to make a successful cut to 170, it would only make sense for this fight to be for a title. So the best advantage for GSP without possibly losing his title is for the fight to happen at around 172 - 174 lbs. But at the same time, people would start questioning how much of a difference 2 - 4 extra lbs make when it comes to how the fight turns out.
I haven't watched it (hour and half, no thanks) but that doesn't make sense. The most advantageous weight for the fight for GSP is 185. No matter what weight it is technically at, Silva has a weight advantage, he is going to walk into the ring at least 10-15 pounds bigger. Given that, better for GSP to have it at 185 where Silva's title is on the line but GSP's isn't, where GSP gets the most credit for winning and where his reputation suffers the least if he loses.
It is the same as GSP-Penn II, there GSP had to risk far more than Penn did. He was the bigger fighter, he has his title on the line, Penn didn't. Now GSP gets to freeroll from the other end. He should be jumping at the chance to do it and as a GSP fan I'm really disappointed that he isn't trying harder to make it happen (not that I believe the 50 million thing, that is obviously bogus) but GSP should be chomping at the bit for this fight and it is clear that he is reluctant.