I've been Arcane for a while, and I was loving it--in my usual raid compo, much less 5-mans, I don't have the people and buffs I need to really support Fire/TtW and I found it boring and unfun. With Arcane I have more mobility, more flexibility, and just plain more fun.

Doing 5k DPS on the 10-man Onyxia fight (where I usually expect to average out at around 3.5-3.8k DPS on a non-gimmicky (i.e. XT, Hodir, etc.) fight sealed the deal for me. Now I just have to wonder if the 4-piece T8 bonus is potentially worth losing my T7--while I don't use the mana gems as often as I used to, I -do- still use them and that 250 spellpower boost is handy for propping my damage up just a little more (I often pop that sucker on XT just before the heart comes in, then the Shaman Heroisms, I hit IV/AP and go insane).

But the bottom line is, yes: Do what you want, do it so it's fun, and while you should always be receptive to advice about your build, don't take anyone's word for granted. Personal experience and enjoyment trump all.