Just something to think about, at least on one bench; I like the steel (thick) to overlap the bench or top of a bottom tool cabinet by an inch or two minimun, so I can clamp on visegrips, or C-clamps to hold something down, on that edge.

I also like a heavy metal top to have at least one corner or edge, sticking out/protruding over the edge.  There are times, you need to slide a piece, over that corner, and pound/hammer on that item. {3/8" to 1/2" flat steel top.}