I’m also on the fence between L and XL. I’m 6’3” and have ridden both the 2019 Hightower and Hightower LT in XXL and they didn’t feel too long, but have never ridden an XL to see if I like it. The reach of the L is comparable to the old SC XXL geometry just a few MM shorter. Jumping up to the XL would make the reach even longer than the older Hightower/LT by 12-20mm.
The only that would be a significant change is the seat tube length, 30mm.
I think the biggest thing that is pushing me towards the L vs XL is chain stay length. SC increases the chain stay on their XXL to account for the added size up front, but based on the geo I have seen for the AM831, it keeps the same length across the board. So I figure riding the L version will give the closest feel to the actual Hightower design.