All the 5400's have the same cab, yes, room for a buddy seat. Actually the cab structure is the same as the 6400's and up and is similar to the old 4300 and 4200's it replaces. Its a good cab, lots of room but not so big you can't see. My biggest complaint is access is tight on the right side, not gonna squeak by the controls all the time.
Sitting in one is probably the best way to check them out. The Challenger 400 series has the same cab structure too if there are any dealers nearby. Controls a bit different.
A note too, the Tier 3 engine w dyna 4 addresses all the complaints you'll find online. The tier 3 adds a pile of power when the
pto is engaged and when in high gears on the road. A new 5445 has more power than my early 5455. A lot of people found the power lacking when they moved from a 4255 to a 5455 because it is a lot heavier tractor.
http://www.ebertwelding.com/groomers...0-IMG_2399.jpg a danfoss model
http://www.quicke.nu/Quicke_NoA/Incl...e%20loader.pdf page 10 shows the EH valve handle that mounts by the armrest.