Ok as a 41/0/20 mage i feel i should comment on this.
reasons i went with arcane.
1) i sit at 40% crit rate all the time, so when i clearcast i'm up to 70% crit rate, as well when something fozen i have 90% crit rate (but i belive crit caps at 75% correct?)
2) when i do crit every spell hits for 50% more and frost hits for 150%
3) i permintaly have 15% mana regen while casting
4) i get 15% more int and 25% more spell damage based on int.
5) AP/PoM give great boosts to damage (tbh i usualy forget to use or try to save for emergency)
6) Slow actually works on most bosses, unlike the slow from frost bolts it will slow the movement of bosses.
i didn't go pure arcane just b/c really not much more i want from there so i chose to go with the ice added part because now i have 90% crit chance on frozne, my frost crits do 150% damage
also anyone who says arcane mages go OOM faster is crazy, 1) Arcane mages have alot more mana then any other mage from talent's as well we have increased mana regen so that improves our mana conservations.