The main functional difference between these two shelters is that the X-Mid uses a wider rectangle (67" vs 42") so it can rotate the inner onto a diagonal. That layout gives much larger vestibules and eliminates the need for guylines because pole locations are no longer right along the edge. Space inside the inner tent is very similar in both tents but the X-Mid has much more vestibule space and a simper (4 stake) pitch. The High Route has the advantage of a very small footprint that can fit into small sites. Besides that there are some smaller differences, such as the X-Mid uses polyester fabric so it doesn't sag in the rain. Mostly I'd decide based on whether you prioritize vestibule space or a small footprint.
(Disclosure: I designed the X-Mid).
Wow, talk about straight from the horses mouth.
I'm certainly leaning toward the X-Mid mostly because I do like the vestibule space, but slightly less expensive and not looking like 10 clowns are going to come piling out of it helps.
It's getting hard these days to find a quality tent with good sewing of all seams and attachment points instead of cheap glue and shoddy sewing. I started out years ago using a Moss tent for backpacking and a VE-25 for base camps that were much higher quality than most tents today. I doubt the current VE-25 is half the quality of the older ones.
