Well.... it's really more about the whole design of the intake both prior and after the port work, in terms of what your combination requires. It's about the call made on the runner length, plenum volume/depth, runner entry design, divider wall shape, and runner cross section and taper. I know.... that's a lot of details. And much of that is just in the selection of the intake itself.
Also, it's about how much the intake acts as a restriction on the cylinder heads. If you have a set of cylinder heads that flow 310 cfm max, and the intake will only flow 240.... what have you accomplished with the heads?
So, for a guy to just throw out there than he can get you 1 mph and 1 tenth.... that don't mean much to me. Obviously it depends on the engine requirements, but to just throw those numbers out makes me suspect... becuase 1 mph ain't much. A change in climate can do more than that.
In terms of the Wilson piece. Isn't that just a cnc fluff job in the plenum? Or are you talking the real 1500 dollar wilson manifold port job?? Again, depends on your engine requirements. It's a generic piece at the very least. It's like buying a box stock carb and expecting the fuel curve to fit your engine requirements.