My list of OLB's:
Fowler
Gregory/Dupree/Beasley you can mix and match. I'm not high on Ray at all. It's a coin flip/crap shoot but I'd be happy with any of the first three. I'd be real cautious on Ray. One year wonder production wise always kind of concerns me. Would rather see a guy produce multiple seasons.
Beasley is the one that concerns me of the group. He demonstrates the least power on tape by far. I wouldn't worry about Ray as a one year wonder as he produced in a rotation with Ealy and Sam the year prior and when he got his chance to start he fucked shit up.
I agree with your assessment Fowler is cream of the crop. He is by far the most complete player as he shows burst, closing speed, a ton of hand power, effective rush moves including a top-notch swim and rip. Fowler has also shown he can rush from any position including as an ILB like Packers did with Matthews this year and he has dropped into coverage.
Behind him Dupree has shown the most versatility but is probably the most raw as far as pass rush is concerned, but that doesn't concern me because Fangio will improve his hand work like he did with Aldon Smith.
Ray to me is the best pure pass rusher at this point and projects well as a 34 rush backer who will be used in space. The only concern I have with Gregory is his weight. If Gregory can put on 20 lbs and move as well as he does now he could easily be the best of the group as his length is unmatched in the class.