Just to wrap it all up - as noted above,
We bought the workbench. It was a B**ch-and-a-half to get put together. Some of the rails were torqued, most of the tabs didn't "slide easily" into their slots. A little McGuyvering with a rubber mallet and a screwdriver worked, though. The aquarium's been on it for two weeks, and I check daily for any signs that the desktop/tabletop is out of alignment, and so far all is just fine.
