That's a stout table! I wish I could build one of that size, but I ain't got no room! Your gusset design looks strikingly similar to the design I just finished welding onto one of my projects....well they're slightly different.

We had 5'x10' rolling tables at work that were made from 2" thick wall pipe and heavy angle, and we used those tables all the time for dropping shop deliveries on. It worked out really well, especially with the massive forklift we had. Many times I loaded 2000lbs. or more onto one table while burning 20 sheets of metal on the plasma table. A table like yours will work for many things besides just welding too.

How do those 5" Harbor Freight casters roll with the weight of that table on them?