If you do any wheeling you might want to avoid using spacers or washers. There are probably guys/gals on here that use them, but that's a lot of stress on a pretty small component. I believe 4" of backspace clears everything on a turn. I'm not sure about 3.5".
My next set of wheels (coming soon) will have 4" of backspace. I will be running 33" tires on a 15 x 10 wheel.