Can I get usable data from my test if I don't hit VSImax?

Yes, you certainly can. In my example, I am going to highlight some of the metrics that may not be as well known as the VSImax number. This can be really helpful when comparing different data sets, as well as showing how healthy your environment is.

VSI Threshold: This is the red solid straight line.

A good way to look at this number is as the (theoretical) number when the VSI Index average bisects with the VSI Threshold it will hit the VSImax.

VSI Baseline: The is is straight thin blue line.

The way this is calculated is by taking a small subset of sessions, say 13 and then we show what our test results look like if we ran a test with only this small subset of sessions.

Putting this all together
Now what we can do is to use the data from the VSI Baseline to get a good sense of how healthy our environment is. You can think of the VSI Baseline as: What does my environment performance look like without putting any real load on the system. Now if you make changes in your environment/workload you can see what kind of impact this has even at a "Baseline" level.