I run 4" X 3/16" slats with no support (84" long) on our plaz/oxy table. You are right in saying it is for the oxy, My HT1650 plasma can production cut 1/2" like butter with little damage to the slats, but the oxy set-up can cut up to 10", maybe more. That said, I thumb and eyballed the build to support a 4" plate placed anywhere on the table. When cutting with oxy at slow speeds, it tends to bite deep into the slats. when cutting 1" plate, the flame can nip about an inch deep, with 2.5" it will get at least half way down the slat. Water changes everything. It will slow the oxy/exothermic reaction some I would suppose, I have not had a chance to finish our watertable.
plain ol bills's water table is the coolest (his table is tooo, but that watertable, wow)
WSS