How high are your ceilings? Is the room open to other areas?
Overall room VOLUME is more important than square footage... Low frequency waves are omnidirectional, they will go wherever they want!
For 2 subs under 1K?
If your room is closed off, with 8' ceilings, you are just under 1400'^3. I would look at Hsu, VTF2 would be very strong in that space. These will likely be your best value for good, high quality Woofage.
The VTF-2 MK5 subwoofer is Dr. HSU's best value subwoofer. Deep bass that doesn't compromise, making it the best affordable home theater subwoofer on the market.
www.hsuresearch.com