Numbers below the cut.
For the sake of comparison, I'm going to assume 0 procs in either rotation. For cast times, I'll use my own Spell Speed (1043). I'm also cutting out Thunder casts, because it's a DPS loss to use Thunder 1 while getting 0 procs.
First up:
F3 in UI3 = 240x70% = 168 - 2.24s
F4 in AF3 = 280x200% = 560 - 2.68s
F1 in AF3 = 180x200% = 360 - 2.24s
B3 in AF3 = 240x70% = 168 - 2.24s
B4 in UI3 = 280x100% = 280 - 2.68s
Rotations:
With 0 Fire III procs, the standard rotation looks like:
[UI3] > F3 > F4x2 > F1 > F4x2 > B3 > B4
F3 = 1 - 168 @2.24s
F4 = 4 - 2240 @10.72s
F1 = 1 - 360 @2.24s
B3 = 1 - 168 @2.24s
B4 = 1 - 280 @2.68s
Totals - 3216 @ 20.12s = 159.84 pps
Yours is (assuming optimal conditions):
[UI3] > F3 > F4x3 > B3 > F3 > F4x3 > B3 > B4 > F3 > F4x3 > B3 > F3 > F4x3 > B3
F3 - 4 - 672 @8.96s
F4 - 12 - 6720 @32.16s
F1 - 0 - 0 @ 0s
B3 - 4 - 672 @8.96s
B4 - 1 - 280 @2.68s
Totals - 8344 @ 52.76s = 158.15 pps
That modified rotation in its optimal situation is approximately even with the standard rotation in its least optimal situation. A single Fire 3 proc added to the standard rotation turns it into a drastic gain overall. The only reason you'd be seeing gains with that rotation is if you're getting lots of lucky F4 crits or if you're performing the standard rotation sub-optimally.