I have experience with two large models:
the first spans 80" and came in at 12 lbs. It was not scale but it flew fantastic with a 90 four stroke. I flew it with a 60 glow and it was under powered. The key on the large models is not the line length, but the AMA wants you to have lines that are 65-70 feet long for competition. Generally I fly the large models with 60' lines with no problem. I have since converted this model to the E-Flite 60 electric motor with a 16" prop, 6S battery it flies at 1/2 power with no problems.
The second was the Sig 1/4 scale Morrisey Bravo, 87" span, 90 four stroke and it came in at 15-16 lbs, flew great also.
The main thing to remember is the adustable leadout guide wiill keep the line tension within reason. If the model flies really fast and weighs 14 lbs it will pull really hard, but larger models fly slower than smaller models. I start with an adjustable leadout guide and move the line guide forward until I have enough line tension to keep the model out there, but no so much that I have to use both hands.
I flew both models with one hand, while the other hand was on the electronic controls transmitter on my hip. If you have to use both hands to hang on then it's flying too fast or the line guide is not adjusted correctly.
If 87" is not large enough consider building the Sig 1/3 scale Spacewalker at 103", A friend built one for CL scale (and still flies it) and it comes in at 18 lbs and it is flown with one hand. again the line guide location is critical. Grant flies this model with the E-Flite E-160 electric motor, the motor is as large as a soup can.
....the 72" span is a great size and the 60 should pull it no problem, just try to keep the weight under 10 lbs.
Bigger flies better.
Fred Cronenwett