backspacing help wanted

I am trying to figure out what backspacing I will need with my setup. I am going to run a 2in. lift, 30x9.5 bfg a/t's and 15x7 rock krawler wheels. I was wondering if I should get the 4.5 or the 3.75 backspacing. I would like for the tires to be about flush with the flares, I dont want them sticking out though.
Thanks

probably the 4.5
I run 34x9.5 TSLs on 15x7's with 3.765 of BS, the tires stick out about 2 inches past the fender sheetmetal, I don't have flares.
They do tuck nicely though, and if you even plan on going to a taller tire the 3.75 will keep the tires away from the control arms.