I'm not saying running out of energy is a bad thing and I'm not talking about coming out of berserk with energy. I'm trying to determine the best use of berserk while it is active. Here are a couple quick dummy tests I did only for the duration of berserk:
What exactly are you seeing that says the Berserk glyph it the way to go now? I don't really see a difference in the dps between glyphed and non-glyphed berserk here. I understand from the 4.1 forums that Glyph of Tiger's Fury and Glyph of Berserk were close. I was using Tiger's Fury prior to 4.2. If we should be using Berserk now, but I'm running out of energy at ~10 seconds, it's basically just like the non-glyphed berserk. From the glyphed tests, it does seem that the shred spam is too unpredictable as well.
As Melthu points out, your 10 minutes of target dummy testing mean nothing. We're lucky as cats to have a very good simulator, Mew, available to us to test just this sort of thing, I'd suggest you grab it and throw in your stats and test swapping Berserk and TF glyphs till you're satisfied.
Even if you run out of energy 10 seconds before Berserk ends, its not 'basically like non-glyphed berserk'. You still get 50% ability costs for that duration. You're still able to do double the attacks during that period you'd do if you didn't glyph Berserk. I don't understand your comment about 'spamming shred is too unpredictable' either. The best use of Berserk as you ask, is just keep up your normal rotation. Keep your bleeds ticking along, the difference is you get to spam more filler, and as a result generate a lot more CP that lets you easily throw in FBs without risking SR/Rip downtime.
I think most switched to Berserk after 4.1 hit. TF glyph desyncs it with Rake/Synapse Springs which can cause some issues and make it a lot more fiddly to use, having to judge if its a gain when TF comes up to overwrite your existing Rake. 4.2 buffed it even more with the addition of an extra 5 seconds on the end (which is still a few extra Shreds) not to mention the impending 4 piece T12 which some may even have already if they lucked out in BH.