Kiex, I would advise on you buying a 19" rack e.g. rittal, new or secondhand. Get some secondhand rack server cases, transfer your CPUs to the racks. It will be much easier to manage thermally, as well as physically. If your room has a door, a small vent at the top and bottom will also help "chimney" heat out of the small room.
That's a great idea but those suckers are expensive - even used. Also, if you want to oc you need room for cooling gear whether you go air cooling (especially) or water. Water gives you more flexibility though and I've seen setups with 6 motherboards on the same pump and radiator. If you go with 4U cases in the rack, you'll have nearly as much room as a mid tower case but mounting something like a True 120 is going to be very tight and you might have to leave the lid off.
In the summer I have a problem with the small room where my desk is. It's 10 x 12 feet and only has one register for the central a/c.
I've found the best arrangement is to have one fan mounted near the ceiling in the part of the room farthest from the door. This gets pointed in the general direction of the door. Then, near the door, mount a very directional fan near the ceiling and have it aimed at about the middle of the door way.
I use
this one or something almost identical. It pivots to point in almost any direction. The arc is about from 40 degrees below horizontal to maybe 70 degrees above.
What happens is you get warm air near the ceiling being forced out and cool air near the floor sucked in. When both fans are on high, they make a bit of a racket, but you can actually feel the breeze created by the cool air rushing in.
It's not perfect, but I can keep that room to within 2-3F degrees of the temp in the hallway.