I use a 5000btu a/c in a 4x8 room and use 3-600w aircooled lights, and I wish I went to a bigger unit. It does cool it down decently, but it takes so long to cool it in the latter part of the light cycle that the a/c heats up the bedroom that it's in quite a bit since the door is closed. And since the air is so hot, it doesn't cool the condensor coils very well and it takes the a/c longer and longer to cool the grow room down, which in turn makes the bedroom even hotter because its running for so long. But a bigger unit might heat the bedroom up even more. Or it may cool the grow room down faster and not need to run as long. They aren't that expensive, I think your just gonna have to try it yourself if you've already bought it and see how it works for your situation, but I would get a bigger unit.
It wont act as an intake though.