Event with a large lens

First off - Welcome to the forums!  I will say that I have the Nikon 200-400 f4 which I have had longer than the Nikon 200-500 has been out.  I have mostly used it for shooting sports but I've used it for other shots where I have needed the reach.  A fellow photographer picked up the 200-500 and as a general comparison, it didn't focus as fast and didn't have quite the IQ as the 200-400.  That said, it did have more reach and was less expensive.  

The biggest issue you will have with either of those lenses is the aperture.  I am assuming you will want to shoot without using a flash and they are long, dark tunnels .  I've used my 200-400 indoors but you will have to sacrifice on ISO or shutter speed.  Unless you are shooting from a tripod / monopod, you are going to need a fairly high shutter speed to avoid camera movement.  If you are planning on using a flash you will need to be sure the flash has the reach from where you will be shooting.

If you can live within those bounds I think you will be happy.  Otherwise you will be fighting with it and disappointed.  If you decide it is too restrictive, then take a look at the 300 or 400 f2.8 - you can find used ones that are not as expensive as new but none of the lenses mentioned are exactly cheap.  Note that there are also decent lenses in the 150-600 range from Sigma and Tamron that will fall into the same category as the Nikon 200-500.

IMO and experience with events, not a good idea… too long.

I would suggest you consider the 80~400 ƒ4.5

That is definitely an option as well.  I would probably go that route unless the f4.5 would be an issue.  

I do events with the trinity and two bodies in my
bag and the 300 ƒ2.8 on the shoulder — to be
mounted on a monopods for mobility or a tripod
when a stationary position is possible.

Some examples of a blues-rock concert: