Nex 7 concert lens ..what one?
Your headlind : "Re: Nex 7 concert lens ..what one?"
'Which one?' is that what you meant? Otherwise, what does "What one?" mean to you ??? I am confused a bit ... or did you mean "watt one", i.e., wanting to bring camera and high wattage lights? Or ...
The most musical lens would be the best one to take.
Which one sings with its, through its bokeh? Why do I ask this way: you will have problems with light (dark), so your lens will be wide-wide open and the bokeh will set the stage of your shots. At 10 + m you will need to have a long fast lens, maybe a 60mm f/1.2 or such (1.5 crop factor). Or you can just shoot the audience's backs with a wide and nice bokeh lens and the band as accessory hidden between two heads ...
How about taking your fastest lenses and switching lenses as the music heats up and you see pictures develop?