If you're going to base the boxing part on one fight, then I think the fairest comparison to MMA is Silva/GSP. That is the one fight everyone in MMA wants to see and it's not likely to ever happen.
You are aware that those two guys fight in two different weight classes┐ If they were in the same weight class they would have already fought a long time ago. The fight between those two is in not at all comparable to Pacquiao vs. Mayweather who just don't get their negociation right.
As for boxing vs. MMA. MMA is still a pretty young sport and not really known outside the US, Brazil, Japan and maybe Canada. You can go at almost any place in the world and when asking any average guy on the street to name a boxer he will come up with Ali, Tyson and the likes. When doing the same with MMAm the average guy probably won't even know what MMA is or would still have that image of "that barbaric fighting with no rules". But the UFC has done a lot for MMA. In the US it's growing more and more popular and with time it may also in the rest of the world.