NYC you'd better get an 8k, BTU. It really depends on where you are, are you on a higher or lower floor?? I have one in my bedroom, it's only a 12x14 room, but it's on the top floor, and the 5k BTU I bought last year didn't cut it. I have small windows too, so the largest I could get (before spending $500 for a vertical unit) was a 6,500 BTU w/a 9.8 EPR. It's a Fedders/Walmart/Goldstar brand. It was $150, it works fine.
Another thing to take into consideration, how much good, clean power is available nearby? Is there good power in your building? How many heat sources do you have in the room? I've got 3 Monitors, a TV, Fridge, and 2 CPU's sometimes running all at once, and it heats up quick!
I have a dedicated circut I had to bring up from the fuse panel in the basement (20amp, ran 10/3 all the way), and it just so happens that the Leg of the 220 I ran the circut off of had very little on it. It still only got me to the next room, so I used it like it was for about a week, then went out and bought some 10/3 cabling and made a nice heavy duty extension cord to get me the rest of the way there. (yes it made a difference)
I even replaced the 18/3 that was originally wired to it, with 12/3. Sorry, but 18/3 is not enough to cleanly draw the 10.2 Amps required every time the compressor kicks in.

Even though most 5-8k BTU's are a single phase motor, they still need lots of good, clean dedicated power.