^True, but a 600 will *barely* cover 5', and will be insufficient, around the outer edges. Go with 1000 watts, if you're serious about using all the width of your growspace. A 600 will cover about 4' x 4', and still have sufficient intensity. I use mine for 3' x 3', maybe a couple inches more. Personally, I'd go with two 600s, (or 400's) if that's an option?
As far as reflector design goes,... I'd look for something that'll disperse light in a rectangular pattern, if you're illuminating a rectangular grow area. Most are designed to illuminate square areas, so you might have to do some searching to find what you're looking for. As mentioned, light rails work great. I use one, and love it. A 600 on a light rail, would be perfect.