With money no object I'd go a GT3RS or GT2 over a GTR. I enjoy driving and learning what the car can teach me about the way it handles under different conditions, the 911s have this sort of feedback in spades. I haven't driven an R35 so I'm not sure whether it could match a 911 in this regard, but I drove a few of the 996 series 911s and they really are a great drive, you have to treat them with a bit of respect or you can end up in the scenery.
I get the impression from most reviews of the R35 that it turns even the most lame steerers into driving gods, this not a criticism, but it's not the challenge or the sports car experience I'm looking for.
I'd reckon the Porsche would be harder to drive at 9/10 10ths than the GTR would be. A generalisation it may be, but if you can drive a 911 at its limits, you could probably get the best out of most cars.
It would be interesting to see what Jim Richards could do with an R35, he might end up winning Targa Tassie again.