Figuring windshield size, Cali 1400

[toaster404]

My 1400 Cali came with a barn door screen.  With laminar lip and big lowers it does fine.  Sometimes too well, and I get hot.  Took it off at one point and my mileage improved notably.  I have an extra screen from another bike in great shape that has the same curve, and I can cut it to fit.  Trying to decide how wide and tall to make it without doing the endless trial and error until it's too small!!  Any suggestions?