In reply to Armadillo:
> The TX5 is stiffer (presumably because of the lining)
Ah, no - the TX5 is generally designed to be a stiffer shoe. It's the far end of the TX approach series and mainly aimed at distance hiking with some capability on more technical terrain. For this reason it uses a stiffer sole and more robust upper materials which help to offer more foot support and maintain the lifetime of the shoe but do mean you lose on flexibility and general tactile feel.
> comes up a bit tighter on sizing.
This could be related to the GTX but unlikely as the membrane is very thin. Perhaps more likely is that the increased stiffness of the upper materials leads to a perceived increase in tightness due to the shoe conforming less to the shape of the foot. The extreme end of this is the need to always size up 0.5-1 full size compared to street when choosing big old school leather boots as these are the least conforming and therefore need more space inside to feel comfortable. Thank goodness for modern shoe designs!