Just to give you some data points:
Masters Nationals 2016, Indianapolis, 45-49, 333m concrete
Points Race, 5th. Gearing 51x15. Probably fastest out of all the riders in a sprint, but missed the main move.
Scratch Race, 2nd. Gearing 53x15. Gambled on it all staying together, which it did. Had to follow an attack w/ 2 to go, chased 10ft off the back, and had 1 rider come over the top when I launched. In retrospect, 52x15 might have allowed me to respond better.
Masters Nationals 2018, T-Town, 45-49, 333m concrete
Scratch Race, 2nd. Gearing 53x15 equivalent. Break of 5 riders. I was stronger this year -- gearing was fine in a break and also gave me a huge top end. Just out maneuvered.
In the US, the fastest Masters track races are usually the 45-49. Usually the younger and older will be slower. I'll see about changing my gearing when I move up to 50+ next year.
I think Queerpunk's advice is spot on. Bring a bunch of gears and you'll get a good sense by the second race of the evening. However, I can say that when you're not fit, every gear feels "wrong" while if you're going great you can ride well from a greater variety of gears.