Bike fit / correct riding position

Maybe ping Scherrit an email to ask?

If you were racing XC then you'd probably worry about them being the same. If you're just a hobbyist then you can probably cope with differences. I know mine are different. But I don't do any big miles on the MTBs. You tend to be able to get a lot more adjustment out of an MTB frame (sloping top tube + more seatpost) so you're mostly looking at how long the thing is gonna be. But then you'll likely be running much shorter stem and much wider bars so I dunno where it puts your hands relative to a road bike position, I just adjust mine until I like them. Test ride?

MTBs are tricky. A wider bar has the same effect as a shorter stem on a road bike - it brings your upper body forwards - so it depends what width bar you'll be using. Which in part depends what terrain you'll be riding, which also determines the seat tube angle. And that's going to depend in part on how long the front end of the bike will be. And whether or not you'll be using a dropper post. Internet bike fits for road bikes are hard, but I reckon they're even harder for MTBs. Another trip to Scherrit sounds like a good plan.

Not sure on the Karate Monkey, but the trend these days is to size up and use a shorter stem/wider bars. Saddle should likely be further forward than on your road bike to aid seated climbing. Most MTB seat posts are inline. Dropper seat posts are quite long so bear in mind the seat tube length, shorter is better so you can use a long dropper post. Flat pedals and feet placed in the mid foot position offers greater levels of control off road, so if you currently pedal with the balls of your foot and "toes down" then you'll need to drop your saddle quite a bit. Shorter cranks can also be beneficial to help avoid pedal strikes.