Watts are watts. 250w of T5 will produce essentially the same heat as 250w of MH. The only energy not turned into heat, is either used and transformed by your corals/algae, or it leaks out in the form of light (out of the sides of the tank or from the canopy).

Let us not forget the First Law of Thermodynamics: "Energy is neither created nor destroyed...".

So, saying "250w of XXXX is hotter/cooler than 250w of YYYY..." makes no sense.