Because "Gig" photos were one of my main interests,way back (1979) when I was geting my main gear,I especially looked for fast prime lenses. I had a Mamiya DTL 1000,whic is a M46 mount all manual but with spot meter. I got a pair of Sigma YS mount Teles,the 135 F 1.8 and the 300 f 4.0. They both use 77 mm filter /cap etc and weigh a ton on that body. However...I can shoot color at asa 400-1600. These old Sigma's though multi coat are a tad soft and low contrast wide open.....but then in a "gig" shoot you tend to have an EXCESS of contrast. Daylight....either lens needs to be around f 8 to seem sharp and saturated,but low light they still do very good work. I (finally) got a "modern" camera....well....a few,and discovered I even have a PK adapter for YS, Looking forward to using the ZX5 Pentax with the Fat Tele's...spot metering too.
I used to do Tri X with a developer called Diafine that did a beautiful push to asa 1600. That made "low light" easy. Now (room mates) I can't set up my darkroom gear...probably forgot most of my skills...shoot color only.
Something to note....sometimes the light guys lean heavy to using the red spots. You tend to get used to it-but on film the effect is pretty monotone as if you redded up a B+W in photoshop. It further tends to wipe out the contrast and make ideal exposure difficult. Blueish spots or a mix with some white or blue will still give you some skin color and color detail in general while also a more natural contrast. It's easy to focus on the "moment" and forget that in photography you really are not taking a shot of a person-place-thing. You are taking a shot of LIGHT. The eye will "adjust" to lighting shifts...film sees just what is.
Getting up close is the key. I prefer a bit off center. Dead center and a vocal mic will tend to often be in the way. With a group where you may want to get 2-3-4 guys into the frame,a little more off center helps,though you can run into depth of field issues.
An annual thing for me is the Hardly Strictly Bluegrass Fest in Golden Gate Park,SF. It's about 5 stages,50+ artists/groups and 500,000 music fans and their dogs or kids. If I'm going to be moving from stage to stage...I can't carry too much or I won't make it through 2 days at 10 hrs each. I can arrive early and take up a decent spot at one of the midsize stages,but once the set begins....I won't have much mobility.
The main stage has a barrier in front. Security MAY let you have about a minute and a half to get a couple quick shots up front. However...my housemate is handicapped and the handicap section is up front and to the side...a pretty good spot for a base camp.
At that festival....I know the location now,as I know our local music club. That helps a lot.