The SWT▸ units have OEM 158 / 159 seats in them but with extra padding. Nice and comfy on the posterior but a bit tight on legroom as the seat pitch is the same as previously. Not sure I could hack 3,5 hours on one.
Tend to agree - Salisbury to Basingstoke was about as far as I felt comfortable with on a 159. Although I changed into a Voyager at
BSK▸ which wasn't exactly an upgrade.