Back spacing on front wheels

I'm running a 18X9 and have 6"+/- back space. With the 73+ disk brakes and the 11-3/4" rotors.

If it was me I would get the 5" backspace can't go wrong there with an 18" rim IMO. The 4.5"B.S. is going to be getting close to the fender lip maybe even sticking out a bit.