Agree 1/4 is more than enough for welding and basic top. If I was going to do the whole top I’d do it in 1/4. Can’t afford to do that. Don’t like the feel, feedback, or sound of smaller 1/4” sections when having to pound something out. Not making the whole top metal. Only a work area. Was going to settle for 1/2, but the plywood top will be 3/4 and wanted the metal to match the height. Doesn’t need to, but would be nice. I used a 3/4” top bench for years pounding out large brass outboard props, straightening flat stock and rods and love the feel of it. Absolutely no give and deadens the sound. To get it done I’m going to throw a finished plywood top on until I can decide how much metal. I’m leaning on two 2x2 3/4” sections welded to the frame equally offset from each end to help balance the bench.