If you're serious about metal halides, at this point I would go Quanta Atlas. A LOT less heat involved, 2 cables to run, 0-10v control, etc... Seems a no brainer.
I still say that from the looks of your canopy, the 5 bar Helix would be way more than enough, easy to mount, etc. There isn't any feedback yet because they just started shipping the bars this week. I will say, the Quanta Pro bars had great reviews, and these are "better" from both a spectrum and a control standpoint. I'm ordering a pair to run as fill lights on my tank.