I live close to proper mountains (the Japanese alps), and did do a few smaller and bigger climbs. The bike felt great, no complaints whatsoever. It is super fun on the downhills, it wants you to carve the corners yet feels safe and secure. It is just such a balanced bike that does a lot really, really well.
Again, I’m taking nothing away from the R5, I have no experience with it. But if this is your Plan B, you won’t have any regrets.