We chose to do 5.5 feet in the middle, with 3.5 at the stairs and 4.5 at the other end. Went with the 5.5 depth as we are taller than average. After the gunite was shot we realized we made a big mistake by walking around in the shell with a laser level to simulate the water level at night.
A majority of the pool was over 5 feet deep, and the parts that were not too deep were too steep to stand on comfortably. We ended up having about 20% of the pool being useable.
There are a lot of variables such as pool size, shape, the way the crew forms the bottom, etc. Based on my experience I would recommend a max depth of 5 feet. Anything deeper and people can't stand up and hang out, but it is too shallow to dive into. I would also recommend being around they day they shoot the gunite and checking depths / slopes. If you want more gunite when the truck is onsite it is cheap. Having the truck come back out costs a lot since they have a minimum charge.
We decided to spend an extra 2k to have the gunite crew come back and fill it in. Well worth it.