me too, this is why I went to a 14 tooth. though I'm a back road rider (not slab)
I use the stock 15 tooth. I don't at all mind revving the Wee's engine, and only use less than 5000 rpm at lower speeds when it doesn't look like I'll be in need of what hard acceleration the Wee has. I just find it's much more responsive above 5000 rpm, especially when I'm riding the twisties hard. I still get 53 mpg riding like this. I will try the 14 tooth at some point, and might just like it.
I may try the 16 at some point as well. If I do it will just be for the fun of trying something different, I think. I honestly find for the few times I'm cruising at 130 KPH (80 MPH) for a half-hour or so I'm not running the engine too fast. Actually, I get so beat up by wind at that speed that what the engine is doing is of little concern, as long as it's not blowing up. Really, this accounts to so small a percentage of my riding time (and a much smaller percentage of my riding pleasure) that I'm in no hurry to change the gearing to slow the engine a bit. If I was commuting at those speeds daily, a change in gearing, windshield or bike might be in order. But I'm not.
I created a gearing spreadsheet for the 650, showing every combination between 14 and 17 at the front and 41, 43, 45, 47, 50 and 52 at the rear, and how they compare to stock gearing (15 and 47), and also showing different rpm at a few select speeds, and resulting speed at 5000rpm. The stock DL1000 comes in at one of the extremes on my chart (17 and 41), a full 30% difference in gearing, btw, from a stock DL650.
I did this so I could better follow the informed and uninformed debates on this site, and cut the crap from the real. But then I have an engineering degree and can be just a bit anal.
My spreadsheet shows that at about (a gps corrected) 120 KPH (75 MPH), I am running about 6000 rpm with stock gearing, and would run 6429 and 5625 with 14 and 16 tooth front sprockets, respectively. There are sites on the internet that will also give you this information. Or slap something on because someone says it's the cat's meow, it might just work for you. That's one of the beauties of chain drive.