Top 5 would be stupendous, 6-8 great, everything below increasingly meh.
This is assuming that he won't have to change his own race to assist Menchov, if a situation arises in which that makes total GC sense. That would probably sink Gesink's own GC aspirations by a handful of places.
So far his (downhill) bike handling skills have been suspect and he has failed to deliver the reachable on key moments. I guess that not all bad luck was unavoidable. Part of a winner's vocabulary is sustained concentration, and positioning yourself in a way that decreases the likelihood of getting caught up in bad luck. Areas he could improve in, I think. Still, some things can't be helped.
To his credit, he doesn't hide behind events, and with clipped wings he still finishes in very very promising positions.
He will learn, mature, grow stronger. It bodes well. To be a great rider you need to be more than accomplished, though.
You also need that little bit of something that can be added to talent and the learned craft. The type of steely grit that I feel is often missing from very skilled and gifted Dutch riders. That funny thing that the German football team always seems to be able to muster, and seems woefully lacking in the Dutch. When the coin can fall both ways, or is tipping away from you, get it down in your ballpark.
Maybe that is the "soft" you mean, the lack of ability to grab Lady Luck by the jugular and force her down.
I have seen flurries where he certainly shows he has "it", mostly uphill. A little flash just before he straightens up, to force the issue, whichever way it falls. At other times it seems to be left for dead on the tarmac, and he looks unsteady. Or seems to get caught out when sustained concentration might have pre-empted that.
Part of this is maturing, part of this I expect to vaporise when he gets a good kill (ask Evans what a difference jumping a hurdle can make in race determination).
If all of it goes, and the Dutch have finally reached the other end of a long walk through the winners desert, that remains to be seen. Oasis or mirage, time will tell.
It doesn't help that most of us are becoming very thirsty. Some jump on the mere sighting of anything that looks like a palm tree. Others prefer to poo-poo it until they stand knee-deep in water - simply another way to deal with having gone from hope to disappointment in 2 easy steps a couple of times too often. And the taller the tree looks, the more proof of water will be required, just in case.
All eyes are on the Tour. And if he can deal with that pressure and ride comfortably into the top 8, I'll be very chuffed, and sure that a young Dutch challenger has indeed emerged, at last.
And ready to sell my camel to those that are taking to their desert, those looking for a meaning to life, post-Lance. Or for forums where an entertaining win can be enjoyed without having to watch endless reruns of the nudge-nudge-you-know-what-clinic-I-mean skit first.