6000 or 8000 BTU Air Conditioners?

Hello!

I am moving into a 3rd floor apt in the Boston area soon. I need to get four window ACs for the four rooms (minus the kitchen where I am just going to put a window fan). Each room is about 170 sqft. I would get a 6000 BTU AC however according to the Energy Star buying guide, the actual cooling I'd need is around 6600-7200 BTU per room.

I cannot seem to find any 7000 BTU units. Would it make more sense to get 6000 or 8000 BTU units?