For a 55-inch span that creates the 48-inch capacity units the expected deflection is around 0.008” – 0.010” or 8-10 thousandths of an inch in the center of the span. For comparison 1/64 of an inch is 0.0157 inches, or 15.7 thousandths. There will be more deflection in the 82-1/2-inch span that creates the 72-inch capacity units than the normal 55-inch span. It will be a heavy 1/32 of an inch of deflection centered around the joint of the two extrusions, so 0.040” – 0.050” or 40-50 thousandths. This boils down to having realistic expectations. If you’re expecting 5 thou worth of deflection on a span either length you need to spend the money on a full scale CNC router and not a ~$1000 router sled. Even with C-channel stabilization a slab will cup, curl, bow, or move more than 1/32 of an inch as the seasons change.