C Virtually unlistenable. I would like to emphasis that there is more to grading tapes than just listening for tape hiss. There are many other things to listen for. Basically how long the tape is. Some picky tapers want exact timings.
Most people are happy with the length of tape the show is on to the nearest side.
For example if you have a show that fits on a 100 min. It is also a good idea to give some sort of set indication. Most use roman numerals for the sets. Some will indicate acoustic sets with an a, encores with an e. There are various ways of indicating partial sets.