Firestarter macro!

[Allyrion]

In this situation, your options are to use another B3 for 220 potency then F3 without the FS proc - perhaps leading into the double-F3 speed cast if you are good at it.
Or you can use F3 with the FS proc while in UI3 (154 potency), saving you 0 casting time (fast-cast F3 from UI3 vs Instant from FS), and a whopping 133 mana.

Or you can B3 --> Thunder II --> (Transpose) F3
Guess I'm not sold that double F3 is worth the mana.

[Waliel]

Or you can B3 --> Thunder II --> (Transpose) F3
Guess I'm not sold that double F3 is worth the mana.

You lose an extra Fire and two potential FS procs with going double F3: 2xF3 + 3xF1 compared to F3 + 5xF1. You can get a fourth Fire with double F3 if your mana ticks align right and you have at least 248 Piety, but then you have to wait for mana for Thunder after B3.

[Allyrion]

You lose an extra Fire and two potential FS procs with going double F3: 2xF3 + 3xF1 compared to F3 + 5xF1. You can get a fourth Fire with double F3 if you mana ticks align right and you have at least 248 Piety, but then you have to wait for mana for Thunder after B3.

Okay, so leaving out the F3 under Umbral for both and using Kenji's potency numbers.
F1 x 5 (270 under AF3) = 1350 potency
F3 (396 under AF3) + F1 x 3 = 396 + 810 = 1206 potency

So now I'm really not sold, lol. The latter does have a notable time advantage, as it is like 2.5 seconds shorter. However, the above calculation does not even take the two extra potential Firestarter procs into account. Also, if you ever don't get the second quick cast, it's way behind.

Thanks for checking how many casts you get per burn. I was being lazy.