These are the hardest that I have done, not that I have seen/heard about. Rumor/Westway weren't open when I went there (only Claires/Anna) (so I have not done them).
I will be first to admit when I was last at Hunter, K-27 and Crossover were iced over so I decided against it (which is now a few years ago).
Skyward is the toughest I did at Whiteface (Lookout was closed sans for Wilmington trail and the Slides were not open (which I do not have the ability for anyways as of now).
What non-gladed run at Stratton is tougher than World Cup (I have done them all and that always seemed the toughest to me)?
I will be the first to admit that I am as good of a skier as many others here, which explains why my list pales in comparison.
Oh, didn't realize it's the hardest that you've only done.
I mean like at Stratton if almost any of the other double blacks are ungroomed they're usually harder simply because they are a lot longer. And yeah, if we were counting gladed areas, a nice progression that's harder tahn World Cup would be something like Moondance -> Kidderbrook Ravine -> Why Not (short but some mandatory turns required and, depending on your line, can have mandatory cliffs).