I can speak to the 980 GTX, but not to the MT Extreme 400. Kenetreks boot did't fit my heel. I sent back three pair and gave up on them.
The 980 is what I would call a mid/heavy boot. The sole is medium stiff and has good flex to it, but climbs well. Very comfortable to walk flat ground in, but enough stiffness to kick into soft soil on a steep uphill. Great heel counter, and support. They seem to run a little narrow on size, which is good for my foot. I would wear them on any hunt, even sheep. They are a little flexible for sheep, but I prefer more flex.
I have 4 seasons on them, and they are still in good shape. The soles are wearing very well.
Basically the same experience as me.
Kenetrek is a touch stiffer and 10 yrs ago they were my absolute favorite.
Then for some reason they started eating my heels.
The 980s are a good compromise of soft enough to not eat my heels so far knock on wood. And stiff.
I'd say they are on the narrow side.
I'd say they are both pretty close. Mostly going to depend of fit.