Andy the longest ride I have done is 2 1/2 hours. Compared to my Selma, the position on the Yelli is a little shorter and more upright, which makes sense given its pedigree.
IMO if map crossing is the priority it’s not the bike to choose, but I see no reason why it shouldn’t be capable. I rode a friends FF29 and I have a Salsa Selma, in terms of pure efficiency, converting pressure on the pedals into forwards motion, they’re both noticeably superior, but the Yelli is no slouch.
For an alu HT I don’t find the Yelli harsh, but it doesn’t have steel twang either.
It’s not a sit and spin bike, it rewards agression on climbs, get out of the saddle and give it some. I’ve been riding a lot of SS recently so this is no bother to me, actually climbing in the saddle is a bit odd nowadays, but I couldn’t sustain it all day! (I may well SS my Yelli too).