When the stars align, there might be [too much haste] (bloodlust, DI, heroic hungerer and matrix haste procs on top of a haste-oriented reforging strategy). Let's say there is 2100 haste from gear, 1730 h-hungerer proc, ~1830 h-matrix haste proc (assuming the heroic tooltip is also incorrect and the actual buff is about 100 more than the hungerer like in normal). With those, DI, and bloodlust you'll be sitting at 21.2 energy per second.
If you were to rake->shredx3->rip->shredx4->FB (assuming you've just popped TF with your berserk, so you'd want to refresh rake and rip is in there just because).
For this sequence you'd need 17.5+21*3+15+21*4+12.5+(up to 25) = 192 energy (up to 217 energy). We have 10 abilities, so 10 seconds of 21.2 eps is 212 energy, and we will be using up to 217 energy.
However, remove FB from the sequence, we have used ~180 energy over 9 seconds, at 21.2 eps you would have generated ~191 in that time period, so you would have had a net gain of 11 energy before FB, which may or may not energy cap you, depending on how much energy you had when you used TF.