hey, it's FUN dreaming about MH...
Just buy a setup that is matched already, like the pendants you were asking about.
One of the nicest tanks I've seen was a 75 with a 2x150 DE Spacelight hung above the water with an open top. Open tops rule.
He had all the SPS he wanted, and barely a heat issue at all. Your 90 is deeper, though - you could go 250 SE if you felt you needed it.