I am "happy" with them but then I only use them in a greenhouse for vegging MJ and my Chillies. MJ goes upstairs in the sun for flowering. But there was just a report by someone who uses 2x 300Wers fine for flowering as well. My growing area is approx 3.8ft x 2.5ft (115cm x 75cm) and I feel that the two 300Wers are just right for filling out this spot. If I were flowering w/ the LEDs I would probably move my plants tighter, like 3.2ft x 1.9ft. I have no reason to believe that you would have a problem with 2x 600W lights, that's twice of what I have with just a little more space.
The reflectors and also the Mars II are "relatively un-interesting" to me since all those lights have 5W LEDs, so they're the same there where it counts, the only reason to upgrade (for me) would be if I were at some point wanting much stronger lights, say, 1200W or something. Since I am only vegging in the GH...and the lights are (at times) actually too strong, say for seedlings etc., I don't see a reason to upgrade.
That being said, I would gladly take a free light
of their new Mars Pro Epistar 160 for testing
Even if the 60cm for coverage width seem a little on the low side to me. (Then again I THINK one of those lights would be just fine to light out my complete 118cm x 80cm area, also for flowering.)