I'd spec the priest disc for leveling with reflective shield for the rogue. I'd level the rogue as combat for the easymode mob grinding and not having to stealth as often. As for 70 and pvp, i have no idea. My rogue takes up almost every keybind I have and uses them all pretty frequently, while my priest is pretty complicated by itself because you are almost always the focus of melee dps and to survive you have to be paying a lot of attention to what you're doing. To play both at the same time at a high skill level would be a sight to see, that's for sure.