Largest amount of backspacing? Need help immediately please.

ANYBODY? Please....


I have 15x9 Weld Draglites on the back with 5.5" b.s. I am about to purchase front welds 15x7, what backspacing should I get? 3 1/2" or 4 1/2"?

Also, is summit the cheapest place to get some Draglites? Any help would be greatly appreciated!