I had the 346w adv plus, I reccomend that, it's worth $30 for two more t5ho, I think especially for a smaller tank so you could run just the t5ho's for a while before and after the mh
to keep the temp of your tank down, that 250w halide is going to really heat up that tank, you are going to have to run fans blowing between the light and the water surface.
I had mine on a 47g column tank and my tank would go from 78 to 84 some days before I put a couple 120mm computer fans blowing on the water surface. Then that in turn really cranks up evaporation, I was topping off about 2 gallons a day.
Just some things to think about. I would get the 346w , because even sps
would be fine running say the 4 t5ho's like 12hrs a day and only running the halide like 4-6 hours a day. And you could tune the color you want your tank to be with more t5 bulbs.