I can not address a 75 gallon directly, but I have a 58 show - which is a 75 cut down to 3 ft.
My 250watt metal halide was failing so I rushed this experiment (it will run about 10 minutes and then turn off for about the same). Took pictures with the Ray 2, a shop light 2xodno, and my 250 watt. Brightness wise the 250watt is much brighter - but then again it is 250watts (versus 100, and 28). I think the ray 2 was brighter than the odno - but my camera's exif data does not show a material difference (the odno has more spill, so that may have caused the camera data to be skewed).
Since I only went to the ray 2 this weekend - I have no experience to how the plants will enjoy it or not - I have had significant deterioration over the last 2 weeks as the hqi failed.
Please understand, I am bias as I have always tried to keep more than 200 watts on top of my 3 ft tank. I think I was in the HIGH light level, and have probably fallen to medium to medium-high. I will edit this post once I post pictures on my tanks blog.
2x ODNO Shoplight
Please note that these are iphone pictures with auto exposure on. To keep perspective, the first 2 have 1/20 second exposure times - the third is 1/129 second.