Quick question for my fellow deathknights who enjoy soloing.
And what level of dungeon did you start switching over from a a full dps build to more of a tanking build? Right now my main spec is DW Frost with IL382 set, and my blood tanking set is about the same ilevel. I have done up to the Forge Of Souls dungeons (and everything below them) just using my DW Frost build and full dps set but my health is starting to dip lower and lower during some boss encounters.
I use dps gear but tanking spec on everything I solo, including the old ICC heroics. There wasn't a point that I switched; I just never tried it as dps. With dps gear in tank spec (with a dual-wield talent), you will still smash everything pretty hard.
I always go with a bloodspecc and full DPS gear. Hardly any fights require tank gear anymore, I think instructor razuvious in naxx, general vezaxx (HM), mimiron HM,auriaya HM, blood princes HC, might require tank gear if you'r DPS gear isnt that great. And offcourse most off the 85 content requires tank gear if you're already attempting that.
I strongly advise against going as frost/unholy though, since having to heal in those fights results in such a huge DPS loss. Blood specc can push out high DPS aswell if played correctly.