I've got a dom and a BR, bother from hatchery stock (same hatchery even), and other than both being black and white, they don't look much alike (the different combs aside). The rock has a much heavier build and is much lighter in color, overall, than the dom. The dom definitely has a more upright posture and longer and more curled tail feathers; overall a more sleek and less "puffed/fluffy" appearance than the br. Neither have laid just yet (could do so at any time), so I can't compare eggs just yet.
Disposition-wise, the dom is a totally docile bird. You can handle her anyway/any time you want without a fuss, and she often ends up in a lap or on your shoulder of her own accord. She's also good with the rest of the flock, never gets into tussles that we've seen, but doesn't take crap, either. The rock, while also generally friendly, is pretty darn bossy/pushy with the rest of the flock, is quite loud, and does not like being touched.