I currently run a 150w HPS, (2'x2' and 4' above top of media, so about 3' above plants at moment with room to grow). Its not near as hot as you'd think that much light would be, prolly no hotter than your current setup and less than what you say you may be adding. I think you are gonna need more height to get the light above your plants, but depends on your grow style. I like to let mine grow up a bit, and bush out, less lst needed, and easier to pull out and seperate or maintain to me than a scrog would be. You are gonna have to work hard to keep them beneath the light in tight space or else raise the roof on that cab somehow. Having said all that you might be better off sticking to those cfls. The best scenario would prolly be to use the HPS and some of the blue spectrum cfls too.

thats my 2 cents but as usual not worth a penny.