I had a road bike fit few years ago. It doesn't transalte very well to MTB. More so that I'm fatter, unfit, and my mobility needs few more months of work.
Slack-r on the Stache is going to shorten the reach by ~20mm that's why it'll need a longer stem.
The main reason for getting a new frame from EU is brexit. They'll become more expensive next year. No one is making 29+ long, low, slack frames in UK, and going custom is way too much hassle.