Why not get two SolarFlare 200's?
The 400 comes with the UV bulbs, but I don't see that as a huge benefit. I'd rather have two panels that I can have at different heights, and run one plant per panel.
SF200 pulls 160W, SS400 pulls 365W. I'd rather have the 320w from two SF200's and have 40-50W of side lighting, but that's me.
If you already have the SF200, I'd rock that until it's inadequate. If this is the first time you're trying this, maybe limit your investment now and see what you really want once you know what you're doing.
Make the best of what you have, so you can figure out what you "need".