Pretty sure that size (255/50r16) is a car tyre only. I won't be recommending any car tyre for a Rocket. I'll leave that to others. Looks like it would be a tad too fat for the rim though. I've seen a 245 car tyre on a Rocket rim and it seems to fit fine and looks huge.
The bike tyre I run is a 240/55r16 Bridgestone Exedra Max radial. The standard Metz (and Avon Cobra) are 240/50r16. The Bridgestone therefore has a higher profile i.e. the sidewall is slightly taller giving it a bigger rolling circumference. I think this improves ride and the tyre has terrific handling. They also look bigger all round.
I love the Bridgestone - plenty written about it on here - am on my second and can't see I'd ever use either of the other 2 again.
Avon Cobra is also a good tyre. The only issue I had was that it tended to be a bit skittish in the wet. But it was fantastic in the dry. Looks good too.
Metz is OK but wears out fast and the handling seemed to go off quite quickly. While they're new, they're fine (but not terrific).