I would guess that if you make it to similar dimensions as the 1"x2" or 1"x4", it should have similar strength. Unless you're planning on parking your car on the layout, most of us over-build our benchwork anyways. Mine uses 3/4" and 5/8" plywood for roadbed, 1"x4" pine box grid, with the crossmembers 16" o/c, and layout support of 2"x4", 2"x6", and even 2"x8", with 3/8" plywood shelving installed on the bottom cross bracing. The whole shebang is also fastened to the walls. In truth, though, except for the 1"x4", all of the other material was conveniently "left-over"

from the material I used to build my house. A little judicious "over-ordering" of materials ensured that there was plenty of layout-building material.
When I get around to installing my second level, it'll be 1"x2" open grid, with a 3/8" plywood top, supported on steel brackets, bolted to the walls. The only reason for the brackets is to support a number of 4' double fluorescent fixtures, slung underneath to illuminate the part of the layout already in place.
By the way, Ron, welcome to the Gauge.
Wayne