I've got 6×3', but can pull a couple screws and have 6×whatever. The SF4000 says it's good to flower at 5×5, but to me that means 4×4. I've got several other good 100w QB fixtures that I can use as well. I currently have one mounted on each side of the SF. But probably ain't gonna need to fire them up for a while though.
Whatcha think?