Welcome!
At 6'4", 32" inseam and 400lbs, for me the CalSci Large screen works well.
It's not huge but pushes most of the wind over my head.
They do a bigger XL and XL-XW (which I also have) but they are huge and can cause problems with the screen mechanism.
With the Large I can have the screen down on regular roads and the wind hits me at upper chest.
If it's raining or at sustained speeds above 60Mph the screen goes all the way up and that pushes the wind just over my head.
If you plan on doing long days in the saddle, you may also want to consider an aftermarket saddle.
I currently have a Corbin which lets me do 200 miles before my butt screams for forgiveness
The OEM saddle is barely good for 100 miles.
I'm getting a Russell Daylong this fall/winter.
I have one on my C10 and as saddles go they are pretty ugly,.... but OOOOoohh so comfortable.
I also have 1 1/2" bar risers fitted.