Maybe 5.25" backspacing is the most ideal... If you can only choose between 5 or 5.5 you'll never have it quite right. This is why I told you to just go 5.5 and use spacers. Think about it. Adjust to perfection.
OR
Your car may be like mine where it has a replacement quarter on one side that makes the tire tighter to the lip on one side. Again... space to perfection.
