I'm not sure that I'm digging the Roc as much after throwing the Wasp for so long. A Wasp seems more forgiving on releases relative to the Roc - they seem to have a similar flight pattern so it is up to thrower. I feel that I have to throw it differently than other similar mids...I don't know, maybe it is psychosomatic thing but I feel like I have to think about it when I throw a Roc.
The only thing that drives me crazy is I love how a Roc flies when it gets beat in. At the same time it does look similar to the flight of a Comet. Personally, I think I'd rather have a beat Roc (Comet) right out of the box and just have a stable-like Roc (Wasp). My mid game is pretty much all Discraft...Comet, Wasp, and Drone.
I've thrown both. The Core, for me, was a tweener disc. I found it to fit almost right between my Roc and Buzz (as far as stability), but it was also longer than both of them as well. One thing you might want to look at, is the Roc+. Same flight but a better feeling grip wise. I've only seen them in Star plastic.
I keep hearing all this talk of the Buzzz and Wasp. Crazy, but I carry all three. I find them to be totally diff. discs. So getting back to your question. The Core imo is pretty close to the Roc. If you can, throw a friends a few times. It's just to close of a call.
Experiment and see what flys best for yourself. A Core is less stable for me than a Buzzz. I have a ton of snap , so maybe that's why I throw a Roc. There are different types of Roc's also. Make sure it feels right in your hand first. Try one of your friends disc's if they have one.