There are a lot of discussions and recommendations around the interweb about K75s's and their windscreens.
One thing I found that helps a little is to add some spacers under wind screen's mounting holes. A 1/4 inch or so on the lower screws and maybe 1/2 to 3/4 on the top. I use the large nylon standoffs you can find at good hardware stores.
This puts the screen at a steeper angle and moves the airflow up a little.
Adding a Laminar Lip may help if you can't seal the deal on a bigger screen. It won't do miracles but helps some.
I am 6'1" and I found the incremental improvements small, but you may see more improvement.
+1 on the helmet thing, I use a Bell RS-1 and I found it as quiet as a Schuberth I test rode, though the noise had a different character. The Bell does have some wind tunnel testing behind it and is optimized for sport bike positioning. Either way though, you still need earplugs.
Finally, I am not currently using the Laminar Lip, it's in good shape but needs new mounting things which they sell. If you're interested, shoot me a PM.
