IMO, 4x4 meters is pretty small for a PS3 Eye setup if you also want to move around much. It's technically possible to set up in this space but, as noted above, a larger capture space is the main reason you would want to use PS3 Eye cameras in the first place. If you have very little space to perform in, there's not much advantage to going with the PS3 Eye configuration.
I think it really comes down what it is you want to capture and how practical your space/lighting situation is.
We used to record with four-to-six PS3 Eye cameras in our garage, which had about that much available space, but we used the semi-circle configuration to allow for more 'roaming' space. If we used the 360 config, the performance space would be too small for our needs.
The space we usually shoot in nowadays is our living room, which is probably about the same size as the garage but we found greater flexibility with dual Kinect. This is because the equipment itself requires a lot less space than PS3 Eye and it's easier to set up and take down. Sometimes, we use triple Kinect in this space, but that can be pushing it--placing a third Kinect in the room really decreases the size of the performing space. We like reserve this option for complex motions where we don't have to walk around too much. For us, dual Kinect continues to be the system we use most of the time. We still keep our PS3 Eye setup available but we'll probably only use it outdoors in the backyard when we have a really big motion to capture. So far, we've been fine with what we can capture in the living room though--the performance space is probably a little bigger than 2 x 3 m, just deep enough to record a loopable walk cycle. We have a carpet that's about this size in the middle of the room, which helps keep us 'in bounds' when recording. (You can see the carpet in this old video:
Mocap Test with Small Child.)
IMO, PS3 Eye is more practical and desirable if you have plenty of space and complete control over the room lighting. I'm just speaking from my own experience though. Others here may have different experiences with their gear.
G.