I'll admit, I don't know what the temps SHOULD be for a H100, but 40C under load sounds pretty good to me. That's idle temp for a lot of people on the stock cooler.
And you're only seeing a 13C delta, which is awesome.
I'm guessing you haven't OC'd yet because you didn't say so, but if you have, that makes it all the more impressive.
I idle right around 30C (give or take a degree or two difference between the cores) with my 212 Evo, but my Prime 95 temps @ 4.5Ghz are in the low 60's, for comparison. You have PLENTY of room for a very nice OC (possibly 5Ghz+), if you want.