I have a 60 cube with a custom hood as well and run the 14k pheonix on a lumantek ballast. I've never compared it side by side to an M80 ballast but I suspect the lumantek running in overdrive or hqi setting is as close to an M80 ballast as you can get.
I love the color. IMO it has a more natural sunlight look but just enough blue that corals still pop really nice. The fish colors look amazing under them as well much better than LED again IMO.
As far as heat issues go i think if you have an open top its not even a thing. In the summer I keep my house at 75 or less and I keep the tank temp set at 79. If I close the hood the tank will reach 82 by the end of a 6 hour MH cycle. This is with two 4" PC fans mounted in the back running in a push/pull configuration and another small pc fan blowing directly on the surface on a 30 min on off cycle. In the winter I keep the house at 72 and the tank swings from 79-81 with the hood closed.
Now there is something very much worth mentioning. The hood is shallow and was specifically designed for an led fixture.Its vented but at the time MH was not something I had considered. I was an LED guy from the very beginning. I think if I were to drill two more 4" holes in the top of the canopy and run two pc fans exhausting the heat up and out with the two in the back pulling in fresh air I would probably run 79-80 with no issues.
I wont lie there is going to be some heat with 250 watts in that confined of an area but if you vent the canopy well the trade off is def worth it I think. Here are some pics of my canopy for ref.
In case any one is curious I run the Kessil for sun up sun down effect for 2 hours on each end of the 6 Hour MH cycle. I ramp up then turn off when the halide comes on then turn on right before the halide turns off and ramp back down.
Oh and I should point out im also running the ballast INSIDE the hood which doesnt help.
