Yeah, popping Tiger's Fury then berserk right after it is a big DPS gain. Taking Berserk in the FireBear profile out and making it manual use has lowered the DPS a ton compared to the FireKitteh Profile. Sadly, if your mainly tanking and just switch to cat to do more DPS during a boss when theres like 30-45 seconds of no need for a tank, most people won't use major cooldowns while doing that DPS, just ones they know won't be used while in tank form (Tiger's Fury for example). Plus, a lot of the DPS stats is missing when you spec to tank. I think about 8-10 talent points, depending on DPS spec, is missing, which is a big DPS loss.
I notice going from my Feral Tank spec with some DPS talents going to my pure DPS talent spec, I loose a good 8k DPS alone there. Plus, when you reforge, you reforge a lot of good stats to dodge instead of reforging to mastery on gear that doesn't have it for DPS. When my gear is reforged to tanking, I go from 22.2 mastery all the way down to 16.3. I believe thats almost 18% less damage to your bleed effects, is which, like you and I know, 50% of feral DPS damage.
With that, you loose lo much more damage because thats also 18% loss on your crits, which equates to about 7-10k less damage on crits. For example, with my gear specced to DPS instead of tank and I'm in my DPS talent tree, my rip crits go from doing 55k damage down to about 47k. Thats a big DPS loss. Respectively, my reg rip ticks go from 27-30k down to bout 20-22k damage.
See, you loose a lot going from one to another, but it's to cost effective and your guild definitely will not allow you to roll on tier pieces you already have unless the people you roll with already has them. At least thats how it goes for me and my guild anyways
EDIT* I mainly just added the cat profile in there because more people were asking for it and possibly thought it would be quicker to switch. But with you having to hold down Alt to pause the rotation, then push a button, it still takes the same amount of time. It just shaves like a second off cause it auto switched shape-shift forms for you and then auto-resumes attacks.
EDIT2** As to the buff then shifting back, well, I don't think that's going to be needed. For example, if it applies the buff then the raid starts while your already in bear form and your tanking first, your going to go in without rage since it decreases by time. So your still going to have to manually shift out and in again to gain that 10 rage for charge. So why not just leave it out and just leave it up to the player to shape-shift that first time before pull.