Lol.... I found a print out of a wheel cross section that laid it all out for me... I still needed help when I ordered. Oh I solved the BS problem I was having, I was originally looking at the ProComp 98 Steelies but wimped out and got alloys so I didnt have to worry about rust in the winter.

 

Go with the 5.00 backspace unless you plan on getting new fender flares. I have the 255/75/17 tires (not much different width than the 265s) on the stock 6.25 inch backspace wheels. As it is I have ~1.5 inches of width before the tread my on my tires stick out beyond the fender flares (PA law says that the tire tread must be under the fender flares). With a 5" backspace and 265 tires, the tread will be just barely contained under the flares, so if you get wheels with any less backspace your tread will stick out beyond the stock flares and you won't pass inspection. Hope this helps!

 

I have the 16 x 8 with 5" backspacing for my winter tires that are 265/75-16. They do stick out further than stock, but the tread is under the factory flares. I like the look of them better than the stock wheels!

As many others have posted, it depends if you need to pass inspection, the 5" BS is likely better, if this is not a concern less BS would allow for future expansion......