Two questions you should ask
First of all, there is an earlier thread in this forum asking about the Walker Titan 4x5.
I own both a Walker Titan SF and a Walker XL 4x5...but I'm much more familiiar with the former. They are sturdy cameras which really lock down rigidly for focus, and I like them very much.
But here are two questions you should ask:
The XL doesn't have any rear movements (the back standard is rigid).
Are you comfortable doing architectural photography without any rear
movements?
I would verify that 300+ extension on the XL. Without movements, I
couldn't get anywhere near that on my XL (which of course could be
an earlier model).
I assume you're familiar with
www.walkercameras.com; perhaps you
ask Mike Walker what movements you need to achieve the 300+ extension
on the XL. (Of course, I only use my XL with a 90mm lens, so I've never
tried for maximum bellow extension. It's quite possible that I'm overlooking something simple - it wouldn't be the first time!)