Best Backspacing for 315/75

[BRS]

OK, I know 315/75/16 on a '99 F350 has been beaten to death, and I've been through every post, but I still have questions.

I'm most likely replacing wheels with a 16x8 (my current wheels are ugly as can be), and I want to go with 315/75/16 MTs of some kind. Almost everyone says those tires rub on the leafs at full lock, and I hit full lock all the time when parking, so thats not good enough for me (I do run chains occasionally too). Also, I've seen stock backspacing cited as 4.0" and 4.5" (Tank has 4" in his library?) - which is it?

To avoid rubbing, and keeping that size tire, what backspacing should I go with? I see 4.5" and 4.0" regularly, and I may be able to find a 3.X" backspace wheel. If absolutely necessary should I consider a 5.5" backspace wheel with 2" spacers???

Thanks!