You will likely get rub with a 12.50" wide tire and a wheel with 5" of backspace. If you want to avoid all rub, you'll probably have to go with a maximum of a 295/60R20, though a 285/60R20 would likely be a safer bet. Going with a coilover that's capable of a taller ride height would help you a bit on your clearances, but you still likely won't be able to clear a 12.50" wide tire with that particular wheel without dealing with at least a little rub.