I'm running a 400w MH std High-Bay setup(magnetic/expensive ballst), been doing just fine. I believe the std bulb for my unit is a MH400/C/U. I think the 'C' is for commercial, and the 'U' is for universal mounting,ie Vertical or horizontal. You do get better lumen output in vertical(base up) position though. The bulb is a 3700K yellowish/orange.

Check this out for progess.. 35 days flowering tonight, these pic are a few days old.. and I've used the same bulb/ballst from seed til now.

http://boards.cannabis.com/closet-ca...-thoughts.html

Good luck dude