I recently purchased a new 2008 GL1800 and found that even with the adjustment on the fairing set as high as it would allow, that I couldn't go over about 30 mph without overdriving the headlight when low beam was on. High beam was ok, but not outstanding. I did a fair amount of searching to find a way to get further adjustment but hadn't found it. Stopped at my local Honda dealer and asked them and they pointed me right to it and then told me that they didn't know about it until about a week ago!
Once I made the other adjustment, I am set. The link below takes you to a graphic that will show you exactly where the additional adjustment is if you, like me, didn't know. Chances are, everyone else already knows all about this!