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.
Christian / Husband / Dad / US Navy Veteran
Current Jeep: 2009 JK UR (3.8L, 4-spd auto)
Previous Jeep (1): 1994 YJ S (2.5L, 5-spd manual)
Previous Jeep (2): 1997 TJ SE (2.5L, 5-spd manual)