I have no heat issues with my light. You may have a little heat transfer but I think it would be minimal. You are so high up that I think the heat would just go out the top of the canopy. In my case I wish the light was transferring more heat to the tank as my heaters run almost all the time in the winter. A 250 may work out well especially if you run some T-5's as well. I think I am going to try a radium next to see how I like it. Right under the bulb the light is going to be real intense and I would recommend light acclimating LPS and softies there. I moved a torch from a lower light area toward the outer edge of the tank and then moved it to the center and melted it. Something to think about as well.
I did offset my light 4" back from the center of the tank and it mad a big difference with my rock work.
By the way your tank setup up is looking really nice. I like the rock work.