It is difficult to quantify what gear to use, when I started I had a similar situation to yourself, I had two choices 49/51 x 15, 88.2/91.8 inches in old speak, I used the lower for warm up, and the larger for racing, everything from 200, 3000 pursuit 10km scratch and 15km madison, I personally, (not scientifically) find that leg speed is more important than inches and I am currently working on maximum leg speed i.e 120 to 160 rpm for pursuit and sprint, then I am working on leg strength in the gym to gain the inches. By gaining inches I mean during training I time my 100m standing starts, flying 100, flying laps and pursuits on gears in sequence, I judge feel i.e can I get on top of the gear (physically comfortable with leg strength to spin it up to <130 rpmish), then I compare the times obtained, some gears feel good, but the times do not show this. I hope this is of some use, I have not even covered the aspect of racing when you have to pick a gear to race on dependent on the conditions, I have raced my entire first 2 years on 91.8 listening to competitors chat in angst discussing whether the wind/track/competitors warranted another inch or less for peak performance. Even now when I train I carry a chart with combinations and inches, then I write what I'm using on tape and stick it to my stem to remind me.