What size enclosures? I would say go higher rather than lower (Confusing?).
With a lower watt bulb you are only going to get so much heat. If that is not enough, your buying a higher watt bulb (pay twice). Plus side is you may have an extra to expand later.
If you buy a higher watt bulb, and it's two hot, you just move it farther away from the enclosures. Problem solved.