I would say 3 also to make the light look equal but, dependin on your tanks light demands it could be excessive, you may only need 150's. What is your goal with the tank? And go w/de bulbs because you want to, dont kid yourself that your saving money, go with the because of lower heat, or u like they way the look/mount whatever. Whien I redid my lighting I decided to go mogul, just because of the expense of of the initial outlay. The power savings in my situation was less than 3 dollars a month and would of taken 56 months to break even, including bulb replacement differences. I figured within the next few years something new n better will be along
BUT there are advantages to going de bulbs and im not knockin em.