Boyd Coddington Wheel Backspacing

[RKHiPerformance]

I have ordered a set of Boyd's wheels for my car and I need to finalize the backspacing. I am putting a 17x9.5" wheel on the back, and I have heard that I can use either a 4.75" or 5" backspacing. Which is correct? I would like the wheel to fit within the wheel well without rubbing.

Thanks very much!

Rick & Kristi
RKHiPerformance@aol.com