MH, one or two?

Hi,

First a little background. I have a 65 g tank (36" L,18" W,24" D).
Currently I have two small hoods. One houses two 30W normal florescence
bulbs and the other four 36W 50/50 PCs. Some time ago I acquired a few
corals (green polyps, open brain and a cup coral) and started thinking about
upgrading my lighting situation. The ballast that controls two of the PCs
overheated and so I thought this was a sign to upgrade to MH. I just
finished building a nice wooden canopy and bought some aluminum for a
reflector. My question is this: Should I go with one or two 250W MH? I
gathered that since my tank depth is over 20 inches I need the 250W bulbs
but each bulb is rated for 2 linear feet and I have to fill up three. I am
going to cannibalize the other two hoods so that I can supplement with
actinic. Would a single bulb centered into the canopy suffice or should I
pay out for the extra ballast and bulb?

Thanks,
Ed G.