I've got them in a 40 x 60 and they are on 8' spacing down the center truss spreaders (4 lights total). Definitely not good enough to work by yet but plan to add 4 more on each side of center on the truss spreaders for a total of 12. Each "row" will be switched.
I'm using screw in CFL's from Lowe's that are the equivalent of 300W with a draw of 65W 12' off the floor with 20" diameter reflectors similar to the ones available on Amazon but larger diameter. Very satisfied with these so far.