yeah ... those HID throw some massive heat.
i run CFL, (used to run HID, and want to again soon) and i find cfl easier to manage heat... 400 watts of cfl may put out more overall heat than a 400 watt hps, however, i find the HPS "throws" the heat down, where, cfl, as long as i have a fan blowing at my lights, it cools them fast , and keeps the glass on them cool. that coupled with a 160cfm exhaust fan, and my cab temp is kept perfect.
i can feel some decent heat coming out of my exhaust port, but the way i have it setup, the air coming out of the cab, is hotter than the ambient temp. I have the exhaust fan sucking the air right off the bulbs.
i used the basic principle that heat rises, and when i built my CFL relfector, made it so all the lights are contained in a rectangle box, thats coated in white reflective poly, then has a funnel system that the exhaust sucks the air from. so its sucking most of the heat from them and out, while passively drawing through the bottom of my cab with cool new air. works really well.
if i wanted to do it a bit more hardcore, i could add a piece of thin glass below the lights, to create a sealed air cooled hood effect... but, i dont want to loose the lumens.
so.. really.. experiement as much as you can.. and figure out what works for you