On a 72" axle? Umm, no. You'll be just fine with 4" of back spacing. If it were me, I'd run wheels with more back spacing.
I’m running 68.5” axles with the common 3.5” backspacing and I don’t like the exposed ball joints. I will be switching to something closer to 5” +\-. I cannot remember what Dynatrac said the max backspacing is but I believe it’s eother 5” or 5.5”. I thought the reasoning for the introduction of the 72” width was so you could run wheels with 5” of backspacing and still achieve the same wide footprint as running 68.5” with 3.5” backspacing?