what backspacing should i get so that my tires stick out more....

 

If you want them to really stick out go with the 15x10. A 16x10 will only stick out a little, but just enougth to get that wider stance. Check out some of the photo galleries, it is a popular setup.

 

I noticed the other day on Weld's website that they offer two different backspacings on 16x10s in 5 on 135mm bolt patterns. one was like 4.5 and the other was like 3.5. They are the only manufacturer that I have seen with two options. Everyone else has factory backspacing (4.5 inches). There may be others but Weld is the only one I've noticed. By the way, there is a lot of debate as to whether or not 15s will fit on F150s with rear disc brakes. Most people say they won't without grinding the rear brake calipers.