Cam followers on crs is the best, and cheapest for a plasma table. Plasma cutting is a dirty operation, no matter what kind of table you have (water, air evac, or just open), and the super precision rails hate dirt. The plasma process can't hold any super good tolerances, so why spent the money ground rail? On my x axis I have 1 eccentric cam follower to snug the carrage up to the rail. I made 2 6" wheels with a 6202 bearing in the center, these carry the carrage on the top of the rail. Then to control the side movment I put 2 6202's on spindles and used 1 cam follower on the opposite side of the rail to pull the 6202's into the rail. The outboard leg only has a single wheel to hold it up. The reason I made 6" wheels is so if some slag, by chance, gets on the rail the large wheels can just roll over it, and not get hung up. Also, if a little red booger of slag does weld it's self on the rail, no real harm is done. You just scrape it off with a flat blade, and if it's really bad, touch it up with a piece of sand paper. Try that with a thomson, or ground rod.
Just remember the process you are dealing with. With most plasma ops you can get away with probably .05" and still have a decent product, as long as everything is square (x, y, and z axis)