Well I'm knew to the game but from what I read I'm 100% sure some M/Rs use wand/dagger over Staff because you get more mdmg or something but you'd have to compare the stats on wand + dagger vs staff not to mention wand + dagger would cost you a lot more. I also heard that M/R was a good pvp combo because you get another disable "demoralize", but don't take my word on that (i'm new to the game like I said before). I'd just check the elite skills
http://www.theromwiki.com/Mage_Elite_Skills and then decide. Tbh, imo, since you already got M/P the only other good combo for pvp would be R.