As you know, my only worry re Nick is his return. His service game is A all the way, but with guys his height we should expect better results than even guys like Fed and Sampras. The problem is that if he has an extra couple percent in serving - which should be his absolute ceiling in service games - he has to be no less than a couple % points down on returning. Sampras server at almost 89% on games for his whole career, all surfaces, and that is throwing in an awful record on clay.
I make fun of ATP stats, but sometimes they are good for a reality check:
http://www.atpworldtour.com/en/stats/service-games-won
Even though the ATP leaves out Davis Cup and TBs, that data is very close to what I get for any player when I have all the matches and all the games.
We can figure that around 92% is the limit, and that's with a guy who is a lot taller than Nick. 90-91% is probably realistic.
Nick is at 87% now. That's misleading because his career so far is very short, and he obviously has not peaked. But even when we look at this year, on clay, 92% on AS means HCs, because there is really no other surface in play yet.
So checking back we can see Karlovic at the top, again, at 92%. No one is voting for Karlovic to go out as an ATG.
I'm figuring Nick has to get his serving to around 93% and returning at around 25% or higher to be a lock for majors. He can still snag one or two below that, but to be the kind of future ATG we are all hoping to see he has to keep his numbers up for a year, at least on some surface. To me that means more dedication to fitness and settling down with a serious coach.
And for God's sake, get rid of Monfils-type showboating!