The footprint (W*D) of RS2 is literally half of 4000ULF. Which means that you can buy 4 RS2's for the footprint of 2 4000ULFs, assuming they are stood upright.
Seeing how your room is medium sized, I would go with 4 of RS2's.
Your room doesnt have the space for 4 of 4000ULFs.
Heck, you can...