Interesting... I had seen that 4.25" of back spacing was the max. Are your springs and hangers in the stock location? If so it opens up more nice options for people.
An 8" wheel with 4.5" backspacing would probably allow for a wider tire than a 7" wheel with 4.25" backspacing. The same size tire on the 8" wheel would actually move away from the spring by a bit more than .5", depending on variations in the cross section of the tire due to the different wheel widths. You're moving the inside edge of the wheel .25" closer to the spring but the center of the wheel, as well as the center of the tire, is moving away from the spring by .75". I think too many people get hung on backspacing measurements. It's the offset that determines where the tire sits in the wheelwell.
