Yes - 72" is generally too big for the horsepower rating of a 3005. That said - if you plan to set the rear tire width >60 inches - you'll want one wide enough to cover your tire tracks. Then - because of the horsepower limitation - you'll just have to learn to take smaller bites
//greg//
NH TD5030, 861 Ford Powermaster, CaseIH Farmall 35A, 555A Ford Backhoe, S150x SnapperPro ZTR, Polaris Ranger XP800
That tractor will pull a 6' box but it will depend on what you are doing with it as to how well. If you are just smoothing out gravel in you driveway the 6' will be great. Some serious dirt moving may present a problem. You might have to take much small bites. I would however suggest getting one that will cover your tire tracks. Measure outside to outside width of the rear tires and use that as a minimum width of the box blade.
The Frontier 2072 specs say 27 HP minimum. I would say at 23.5 HP, you should consider a narrower box as well. Unless your rear wheels are set wider than 60" overall width, a 5 footer would probably work well with that tractor.
I have a 1978 Kubota DT185L 18.5HP tractor with a 48" blade box. I extend the teeth fully down and have two chunks of railroad tie on the box for additional weight. Works great on hard packed gravel roads.