PS3 Eye cameras may require more space because you have four to six cameras to place. If you're having trouble capturing a full body with the Kinects, I don't think you're going to find PS3 Eye more suitable.
That said, 5 x 6 m should be quite large enough for dual Kinect--your space is just a little shorter length-wise than our living room where we shoot our films, and we have lots of furniture, bookcases, etc., in the background. You can see what this room looks like in this video:
Three Happy Cats.
BTW, RGB color in the background is mostly irrelevant with Kinect because you're actually using the captured depth data for tracking, not color. You do, however, want to watch out highly reflective surfaces and solid black surfaces--I find these surfaces can be problematic for IR. For the most part, however, it's only a problem if this describes your floor and it's less important if it's the far background.
Have you tried placing the Kinects into opposite corners? This arrangement works for me when I wish to shoot 180 degrees, though the corner of the sofa does block one corner. However, I typically shoot 90 degrees, placing a Kinect near the corners along one long wall. This is how we shot the above test and getting full 360 motions was quite possible with this setup.
Tracking, btw, should not take very long. What is the duration of your calibration video? 600 frames should be plenty of frames for calibration. If you're video is much longer than that, try reducing the tracking range in the timeline. If the issue is speed, you may need to get a better graphics card. The card I use is an older GTX 460 but it can track a frame in about 0.67 second. Newer GTX cards are much faster than this.
You mentioned that you wish to capture jumping motions. Since your space is restrictive for cameras at normal height, try positioning the cameras lower and pitched up, or higher and pitched down. You'll need to experiment to see which arrangement gives you better results.
Hope this helps.
G.
