I think your freak will handle whatever you need. Unless you are super concerned about a few ounces or grams, a slight efficiency gain, looks, or just have cash burning a hole in your pocket.
For lightweight the guys are probably right on the deadlywind, though I doubt if actually performs better. Perhaps marginally quieter depending on what size/style freak tip you are using.
for better efficiency: Get a .678 and a .684 eigenbarrel. Both for $80 bucks total. 9" control bore and then step slightly larger for last 5 inches. Better efficiency than a freak because of the longer control bore and then the rest of the barrel isn't huge like a freak. Losts of small porting for quietness. Also one piece which can be a plus. Lightweight aluminum.
really, If I were you. I would just buy a smaller freak insert if you need it. They now make them .675. Or you can get a brass one from tymcneer in smaller bores for a bit more $$.
I have a 14" freak junior and run a .679 insert(underboring by about .004-5) and it shoots darts with good paint in my cocker.
I currently have a .678 eigenbarrel being milled to fit my blazer.