We hadn't considered or observed the side-loading force as being a problem; however CIM motors are cheap enough that it's not a burden to replace as long as it doesn't die completely mid-match, just bring a few spares

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We use a hall-effect sensor to determine our RPM (surprisingly easy to setup hardware for, code isn't too bad either, I can share details if you want to give it a go), and shoot at 3900 RPM (we can get up to 4400 RPM with the wheel).
Aside from consistency, the closed loop (using a fairly simple bang-bang controller) provides a huge benefit to spin up time. We went from at most 1 shot per second (with inconsistency depending on how long we let it spin up), to one shot every .4 seconds, and much more consistently.