Owners manual?! Communist propaganda is all that is... As for cans: yeah, choose carefully. I have it on good authority that most claimed gains in power, assuming there's anything to legitimately claim, are only there at sea level, and often turn to losses at elevation. The stock can is pretty well optimized for the targeted elevation; there might be a little to gain in some circumstances (like sea level, or nosebleed elevation), but I doubt it'll ever be more than a couple HP. That leaves weight as the only thing to really gain (or lose, as the case may be).
Kind of irrelevant but I'm not sure that's true. Outside of the few early 2019 issues the 850 seems to be a really solid motor.
Yeah, I'm not saying it's a bad motor, and it may be that top end life is just as good as the 800 HO (for '20 and later, at least). I feel like the HO has a more bulletproof bottom end though: I see more crankcase carnage in the 850 subforum. Of course, lucky Pro owners get it on both ends... Polaris went back to Fuji for cranks in '13 after all the failures on the Pro; that continued with the HO, but ended with the 850. Anyway, I'd be pleasantly surprised if the 9R lasts as long, on average, as the 850 or HO. Actually, more like shocked: there's no way you remove rotating mass, add bigger pistons, and get the same life. Hopefully it's at least predictable and gives some warning, and it'll be something like 2000 miles of life vs. 3000. That's probably an acceptable compromise for many. For me, I'm not too interested unless it it can equal the 850, especially having just had an unexpected "boom."