Just to close the loop on this. I built the top with 1 1/2" thick 5/4
stock around the edges of the plywood. The desktop came out plenty
stiff. My concern was the overhang but I can barely get it to flex
even putting my 230 pound frame on it. I put 5 coats of poly on the
top so it should hold up as long as my kids don't attack it.

Thanks again everyone,

Steve