Tiny optimizations
-Spamming your Fire3 key on your last fire of the rotation (Assuming you aim for the 'blizz3 at 400-450 mark) will cast your Firestarter as soon as it procs, if it does. Otherwise, do Blizz as normal.
-If you finish casting your Thunder X and you -just- get the MP tick, you have enough time to cast Blizz1 or Scathe and then Fire 3.
-If you're lazy like me, make a Thunder macro; With your "I have mp" thunder cast first, and your "I don't have MP" thunder 1 second. What this does is cast your preferred Thunder if you have the MP, and the cheap one when you don't. Assuming you don't fall under 250something MP after Blizz 3, you'll always have a thunder rolling and get back into Fire as soon as possible.