I found that the 6.5 did not offer enough wind protection although it was certainly better than the stock Street Glide one (what wouldn't be). The 8.5 gave enough protection and I could see over it. I am 5' 8". However at certain speeds it would create a "drumming" on my helmet. It would come and go but was irritating. It might not happen for someone who is a different height or does not wear a full face helmet.

BTW the Klock people are great to deal with. They have loaner screens at Sturgis and I assume Bike Week, and at certain Harley dealerships. Try one a see if it works for you, as it is such a matter of personal preference.

 

The stock windscreen IMHO isn't worth the effort Harley spent installing it to begin with. Bought the 7" HD which is also worthless to this 5'-10" rider on a stock 2010 SG seat. Can't hear the stock radio, can't stop the glasses from bouncing and forget about the ears after 30 mins on the highway. Just ordered the Klock Werks 8.5" Flaire last night and it has already shipped. Should have it in a day or so and will repost with my .02 FINGERS ARE CROSSED