250 vs 175 watt MH on a 75

[down&dirty]

I am not new to this hobby, but I think that my question could help others in their attempts to build a reef. I currently have a 75 gallon tank with 220 watts of PC lighting. It is occupied by a bunch of softies and leathers. I am ready to start keeping some SPS but what I want is a LPS tank that has 2-3 SPS colonies in it. I don't want an SPS tank if I can help it. Just 2-3 that I can put around the top of my rocks to accent the softies below. So what I am thinking is cutting back to 110 watts of PC actinics and 2 MH bulbs. The problem is 250's are not but a few $$$ more than 175's. Many people have said, get the 250's then you won't have to upgrade for a long time. Well, that is all good, but what about the heat difference. I don't want to and won't run a chiller. Will the 250's generate that much more heat than the 175's. My hood stands a total of 12 inches above the tank, and I will be building a new one soon to go in my new house.