I ran my boxxer crowns backwards for a few months last year to try this reduced offset idea. The crowns are offset around 8mm, so reversing them takes the total fork offset from 46mm to 30. I liked what it did to the handling at speed, even with the reduced wheelbase. The only issue was it...
I rode a large for 2 seasons, and a medium before that. I've moved on to newer bikes, a 2012 demo and a 2015 rune, both large and significantly bigger than my large Sunday was. I have long arms for my height, I've always been more comfortable on longer bikes.
This depends on your saddle. With my ibeam setup (on a large Sunday) I had to slam it forward and tilt it further down than I wanted in order to slam the post height. But I'm only 5'8" and had no trouble riding with the seatpost a few inches up.
Their site doesn't work on my phone, but here's the geometry chart for my 2015 rune. There's a .4" difference in BB height between the wheel sizes.
If they compensated for the bigger wheels by using lower dropouts it would also slacken the angles significantly, which isn't the case.
BB height is no different with the 26" or 27.5" dropouts. If you look at their geo charts the BB height is about half an inch higher across the board with 650b wheels/ dropouts. This is why my rune still has 26" wheels.
There's a lot of personal preference involved in frame sizing. I'm 5'9" and I rode a large sunday for a long time. I eventually realized I wanted an even longer bike, now I'm on a large demo. I imagine I'd be pretty happy on a large sunday if I were 5'7".
Compared to modern bikes, the large...
The word enduro covers a pretty broad spectrum of bikes. The fact that you said trail bike suggests we're talking about opposite ends of that spectrum. Your average modern 160-170mm enduro bike is every bit as capable as what was called a freeride bike 10 years ago.