Depends on the brand. The Honda Rancher fuel injected 420 (and the Rancher 350 w/carburetor) ) all had adequate power in CO for what i needed, including high elevation use. Both had 5 speeds with electric shift and were lightest in class machines....but rode rough with a solid rear axle!
That said, I had an Arctic Cat 400 for a short period that was built on a big frame, was heavy as heck and wouldn't pull the steep mountain mining/jeep grades above Leadville, CO. It was jetted for 10,000' but would just run out of power in low range. A buddy ran it for years at lower elevation where it did better. It did ride well with IRS.
These days in BC I really like my 13 year old Yamaha 550 Grizzly. It is relatively light and compact, great with an excellent suspension and seat, fuel injection, independent rear suspension and power steering. I never ran out of power with it pulling loaded trailers through swamps in Northern BC, plowing snow, etc. It is more comparable to the Kodiak 700 today in terms of frame size, smaller than the Grizzly.