Pavlik is a pure boxer right? Unless if he learned take down defense in our hypothetical I think he'd be taken down very easily and either submitted or GnP'd out. A boxer always has a punching chance, of course, but he'd be a significant underdog vs a complete fighter like GSP.
Turn this into a pure striking match and that's a totally different story though.
No **** why do these hypotheticals always have to be "If it was in the ufc cage". It goes both ways. If it was a pure boxing match, GSP gets KTFO by Pavlik. If it's in UFC, GSP should and probably does win. Same with all the bs Floyd Mayweather comparisons. I would take him over anyone at his weight in a pure boxing match, and that includes BJ Penn, Urijah Faber, Huerta, and whoever else at 145 or 155. Throw Floyd in the cage and he more than likely loses.
I actually think a boxer has more of a chance in the cage than an mma guy in the ring. I think a boxers hand speed and punching power can make things interesting in a cage.
In other words, I can't see an mma guy ever winning with boxing rules. I can see a boxer who's hands are so superior that they can be kept from taking down.