I threw money at the problem and got a larger, adjustable "Adventure" screen fitted to my GS. But when I traded that bike for a twin-spark version in late '03, I wasn't sufficiently persuaded by the results to transfer the larger screen to the new GS. My commute to Watford ended in early '04, so I stopped searching. But after 8,000 miles of pootling around West London I'm now commuting along the M4. Having taken a fresh look at wind noise reduction, I thought it might be helpful to share the results...
"The main noise source was the turbulent flow from the top of the windscreen. The turbulence hits the helmet at a position somewhere between the neck or the top of the visor depending upon the windscreen's height. This position determines whether improvements to the sealing round the neck or improvements to the visor and its sealing and hinges will be more effective at reducing noise. Noise reductions up to 8 dB were achieved by simple helmet modifications or treatments. The lowest levels at the ear were obtained under earplugs and under a flying helmet containing earmuffs with active noise reduction."
Meanwhile, I've also investigated the after-market in windscreens that are wider as well as a bit taller than the one I have. BMW will sell me an Adventure screen for about £196, including the screen blocks, but it's only about an inch larger all round, and didn't seem to make enough of a difference in the past. An MRA "Vario" will set me back about £106. Discussion forums talk about additional "winglets", but it's not all that clear that these are necessary. The rather fulsome X-tall Aeroflow will set me back £390, since it has to come from the US, via a French distributor. Finally, Cee Bailey of the US will send their biggest screen for about £240, just under half of which is for the shipping.
I've since ordered and fitted the MRA Vario, having seen generally good comments around the web, and discussed the why's and wherefor's briefly with Giles at HPS, the UK distributors.
I considered a here's-me-hands-free-on-the-M4-"Jackass"-style video clip for proof, but have contented myself with a shot of the the MRA Vario screen from HPS, in situ.
At last, I can hear that flat-twin Boxer at speed, instead of the wind.
Job done!