5 foot wide (x 10) is usually cheaper by the square foot than 4 foot wide. And......you cannot usually buy 4 x 4 sheets without some sort of a cutting charge. I have a 4 x 4 (PlasmaCam) but have configured a support roller system that will accomodate 4 x 8. I wish I had a 5' wide system so I could buy steel in 5 x 10 pieces.
The PlasmaCam software allows you to easily cut parts bigger than 4 x 4 by cutting everything in the 4 x 4 perimeter...then allowing you to index (move) the plate to cut up to 4 x 12.
Of course......the other issue is material handling.....how do you move large plates on and off the table.....another subject entirely for the small, one person shop!