Larry, I would break it in 10ft squares as that figures easily with your slab. I have always been told 1/4 the depth of the concrete is best depth of cut, but our saw is set at 1 1/4 inch so that is what we always do.
Talk to 10 engineers and you will get 10 opinions on how it needs cut though. Had one tell us to cut a slab into 20ft squares a while back and it was just a 4 inch thick slab.
Had another tell us to take the thickness of the slab, multiply that by two and you have the feet the cuts should be apart. So 5 1/2 X 2 = 11 ft. On his line of thinking that 4 inch slab should have been cut on 8 ft centers.