For a room of about 150 sq ft, what would you say would be the best BTU's for a window A/C? 6,000 or 8,000? Which is really necessary? I have a nice 6,000 BTU one and it does the job just fine but I was considering upgrading to an 8,000 BTU, figuring the compressor wont come on as much, maybe being more efficient as a result. This room has one window (A/C would be in it)and faces east if that makes any difference and is insulated, and on the second floor. What do you think?