Would be an entertaining fight even if they crossed paths at different stages of their careers. Prime for prime I think Golovkin is simply the better all around fighter. The height advantage wouldn't matter much as Pavlik is not going to win the battle of jabs. (if there would be one) A technical boxing match should it play out that way GGG wins for sure. If it's a war clearly Kelly has better chances but, GGG seems to have the beard and composure to edge it when things get dicey.
I wouldn't count out the 07 Pavlik, TBH. Golovkin's career is a huge disappointment. He never beat a single fighter during his 2012-2015 reign on the level of peak Pavlik.
I think Golovkin is highly overrated, honestly. I’m not saying Pavlik beats him, but I think it wouldn’t be at all one sided. This one is very close and hard to call IMO.