Nope. Not a chance. Had gs2 before the gnex n while it was a great phone it, like the nexus, was not perfect. Doing anything for more than 15min made it really hot, it took 3hrs to charge, the home button was clunky, while i actually liked touch wiz the icons were cartoony and colour was massivley over saturated. Basically my feelings on it were; whilst there is no doubt it was a power house of a device it was too powerfull for itself hence the heat and massive battery drain and stupidly long charge time... try using navigation whilst charging.... toasty
my point being the supposed specs for gs3 sound cool but find it hard to believe it wont result in the same problems.
The nexus may have a hint of lag at times.. that is unavoidable because of the way android is written... my stock gs2 did at times too.
While the nexus if also far from perfect im with matey above... nexus line all the way for me now. As for updates... ffs. Gs2 has had a couple of pointless updates that havent changed, improved anything. Yep waiting is annoying and i cirtainly want an update that stops the random reboots, id rather wait for this than have an update that fixes this but adds new bugs.
Enjoy what u have, unless you have endless cash to upgrade every 2-3 months youll never be happy.
/rant over