I'm sorry but, there are many parts of that specc that can give you issues... for one, phase out(improved planar shift) is a must. fully specced it is instant, which is very nice. also, fully speccing the dmg decrease for the pact's is very usefull, as with a pot you'll actually be able to use them when you solo, both pvp and pve. greater flames, most have it, it's a nice nuke to eg open up a boss fight with.
well, your featcalc is old, but play around with backdraft, I like it. and Detonation, is a must. as is full combustion.... having 2 insta casts is Very nice.
also, atm there is little point in fully speccing GoH, as it will make the root break faster.... I can understand that you want the imps, but you sacrifice a good root for them, up to you if it's worth it or not.
hells blood is very nice, you should try it at some point, see if you like it....
also..... do you need the specc'd -hate%? it's quite easy to gear yourself with a few gemmed -hate pieces, and unless you do some serious raid dps you should not need to specc for it. it's 5pts you could put somewhere else, ex in archmage to make your 2(!) instants do full dmg.
tome of erlic is Very nice, but I know many consider it not worth the extra points you have to spend... I haven't decided wheather to keep it or not yet, it's mostly a matter of preferenace.
try for something more similar to this;
http://aoc.yg.com/askkalanthes/featP...110-22,4106-25
I did that fast, prolly forgot something..... anyways, there's quite a lot of room to play around with, depending on your playstyle
-Naya
EDIT; and we Are squichy.... we're mages after all. 3 mobs Can be challanging, sometimes. try carefull pulls, in the build I suggested you get several instant cc's, use them, along with the havoc root. take advantage of teh mechanics... cc one, move back, and aoe the two others. use your planar shift(which is Very nice specced) and double-tap. use your pots aswell, they don't cost all that much.