I recently hit 85 on my priest. I'll mostly end up doing heroics and possibly 10 or 25 mans in the future. As for right now i need to gear up. I'm typically shadow, but to save times on wait times i will do most runs as a healer. I'm not new to healer at all, been holy on my pally for a good long while now. so with that in mind and considering what is mostly 318 gear which spec between healing and disc would be the most functional. I tended to prefer disc in the past, but that's when mana wasnt an issue. I keep trying to weigh the two specs and i can't really make up my mind. any suggestions or insight would be most appreciated.

oh and whats the viability of doing like a renew holy priest? plausible or no?