It all comes down to prefeerence and tone really. The tighter the tension on the low B the tighter it will sound. The looser and the more flub there will be. I use a .70 on my 7 string, Loomis uses a .70 for touring and an .80 for recording. The tighter you want your tone to be the hevier gauge you use. I use and .11 - .70 set and tune down a 1/2 step. Ernie Ball's they got just the right amount of bite. They dont last very long but i love em fresh out of the pack. I ususally change strings once every week & a half unless im gigging frequently, then its once after every show.