Actual Hitch Weight vs Dry Hitch Weight

You should not consider the WD hitch as effective in moving the weight to keep you under your GVWR of the truck. Realistically by the time you get a trailer that close, outfit it and hook it up, you will be over. Also they don't transfer as much weight to the trailer as you would think, and the longer the trailer, the less it will transfer. Use the transfer amount as your buffer, fill to GVWR and when you apply the WD it will move you ever so slightly away from it. My guess if you require your WD to get you by, you will not be under your GVWR. If you looking to just be close, over a bit is ok, then this becomes a moot point, just get what you like and don't worry about what me or him or anyone else says you should do.