If you go to this website they have alot of information regarding bulbs and ballasts. While he doesn't rate the bulbs per se, he does provide spectral diagrams for many different bulbs powered by a variety of ballasts. The Iwasaki 15K seems to very well on PPFD (Par) when compared to other 175MH bulbs. I have never used them so I can't comment on perceived color.
What are you using the bulb for SPS or LPS/Softies
I have ben talking to a few ppl on RC that have been using this bulb .Most of themhave SPS ,the one that saw my post that i wanted to switch to the iwasaki said that it will be to brioght for softie /lps tank ,I also sold one bulb tpo an RC member who simply loves it .
2 MR members are using them as well .
samksy ,and denali69 ,hope theyll chime in soon,