Here's a few thoughts: as you noted, the commander is comfy and has good ergonomics. BUT, they get hot in the cab and they are loud in the cab. The x2 should be cooler and it's supposed to be substantially quieter.
The commander has a fast top end speed. 70 +/- a few mph, depending on the particular machine, windshield, roof, etc. The x2 is limited to 52 or 53mph. To remove the limiters, you need this: https://www.wellerracing.com/WR-Edit...4-_p_3860.html
That, with stock clutching and tires will put you around 60mph. Tires, and clutching will get you close to a commanders top speed but probably still slightly less. JBS has clutching for the x2 and x4 - https://jbsperformance.com/?tabid=55
I ran his sheave and weights in my rhino and it was great. Still, the commander is fast out of the box. The 11-17 1000cc commanders have 85hp and the 18-19 have 92 hp. I'm not sure what the yamaha 850 produces. I think the 800cc commanders are 70ish hp.
As to everyday use power, there's probably not a lot of difference.
Coming from a yamaha's ultramatic, you will hate getting used to machines like can am or polaris, which don't use a constant tension cvt and wet centrifugal clutch. The are not smooth when you take off like a yamaha. There's an rpm build up, then the primary grabs the belt, there's usually a clunk and then you're moving. You can lower the can am's engagement with a low speed engagement spring, which helps a lot with this irritation. Otherwise, its best to get on the gas solid to take off, then let off to where you want.
I don't find it particularly hard to change the oil on the commander. It's sort of tedious getting all of the pins out of the plastic to get to the motor but once you get a pin pulling tool and do it a few times, you get used to it.
I suspect that at the end of the day, that the yamaha will be more reliable but you can have problems with a given unit from any manufacturer.
Yamaha comes with doors. Commander doesn't. Yamaha has fully lockable front diff.