I'd go with the 250's simply for the heating issue. With that amount of light you should be able to keep whatever you want. 6.1 watts per gallon is plenty. The 400 watt bulbs are used for deeper tanks, however you could use them with a 30 inch tank, again your heating problem is going to be worse. I have a 150 tank and I'm about to add 3 250 watt bulbs myself with 440 watts of vho
. You will need to plan on adding fans and then still possably a chiller. I would say with 3 400 watt bulbs the chiller would be a must. Just research as much as you can like I have and make a decision you can live with due to the fact of not wanting to redo anything.
It will also depend on if your canopy is enclosed or open on the top as for as the heating goes.