Actually some of us have done this before but we take into account ride height, clearance to fender used, flat bar, or tubing with machined ends. No magic formula.. you build it to suit your needs.
What you asked is a bit like what color should my bike be.. many answers to certain questions.
They will ride rough, but I did this year manage to ride(strutted 750) 660 miles in a day (780 in 28 hrs). I figgered that was ok since I hadnt done any road trips in about 19 years..