I have played seven string guitars before, they're good for wanting to play in the lower tunings but of course it depends on your feel and whether you don't mind the wider fretboard, etc. I mainly use baritone guitars, which have an extended scale length. At first the difference in scale length threw me off a bit but pretty quickly I got used to it. The ESP (or LTD) Viper baritone isn't bad if you're looking for something more comparable to playing a Gibson. A bit neck heavy though. The Schecter or Fender baritone scale guitars are nice and more comparable to playing, naturally, a Strat type guitar. Lately I've been using SIT .13-.62 strings and it's been very comfortable and staying intonated and tuned very well.
I used to play Gibsons with very heavy strings for years, detuned to Bb. I didn't mind the tone too much (though I now prefer the baritone's tone) but I had alot of problems getting the guitar intonated properly especially for playing up near the 15th fret and on. Unless you've got a guitar tech and some $$ for constant set-up jobs like Zakk Wylde, I'd stay away from trying to detune a Gibson (or any 24.75" scale guitar) that low.
If you look around you can find good quality extended scale/baritone guitars for under $500 or $600 pretty easily, notably the Schecters like mentioned above. Good luck.