Really good question. My primary experience with 29+ was on the Salsa Deadwood and the huge diameter and moderately low gearing kicked my butt on long climbs and even short punchy climbs. I felt like I just couldn't get geared low enough. I don't seem to suffer those problems with 27+ but still enjoy all of the big wheel benefits. I think I like my choice of 27+.
It's a tough question and I'd say go with your gut. On the upside, I don't think either choice will ever be cause for regret. I do REALLY love the Muk with those 27+ wheels. So fun.
Thanks! Great point about the gearing - I hadn't considered that. We wander in an EarthCruiser for several months at a time and I'm fiddling with the bikes to take along. Right now it looks like I'll take the Mukluk with 27.5+ and a Cutthroat with 29 x 2. Cutthroat is a wonderful Forest Road bike that handles pavement acceptably well and feeds my need for long mile days. The Mukluk really shines in the desert - the recent posts on "snow crust riding" remind me of playing on aeolian sand. Not sure I'll have room to carry the 4 x 26 wheel set also - there are 4 packrafts competing for that port storage locker...
Howard