Respondents--- mileage is important. Sleds @ 2000 miles can reveal a lot of issues that won't pop up in 3-500 miles.
2020 ProRMK 163, Khaos Geometry, 7" shorter tunnel running MTNTK 5' cooler (stock coolers are not plumbed in)
2400 miles--- no mechanicals
Couple of electrical failures-- Water Temp sensor (twice until the latest sensor fix good now), EGT sensor (same sensor they ran since 2018-- think it was an anamoly)
I would steer clear of a 2019 without the FULL 2020 updates (groove in case/ lockring versus loctiting bearing to case half)
850 motor pulls a LOT different than 800. My initial reaction to riding mine was "uh-oh" thinking I just wasted $15,000.... as the motor broke in, it got stronger and stronger. After rebuilding one of my 800s, I was able to ride them back to back in the same conditions. The 800 is snappier and revs faster, the 850 just PULLS like a freight train. Pulls a lot harder in deep, steep trees.
Will be transitioning my personal sleds (four Axys 800s, one 850) to all 850s.