ABS is definitely a worthwhile upgrade. I wish I had it (I have a 2006 wee). Anyway - my Wee's gearing is stock, and I'm occasionally surprised while cruising around, or commuting to work, that I'm in 5th gear, instead of 6th gear. I usually get a reminder that I'm not in 6th when I overtake a slower moving car, and the bike leaps forward, instead of oozing forward - dead giveaway! Even with the stock gearing, the Wee is still smooth in 5th gear, leading one to sometimes forget the final shift to 6th. You could even gear the bike down from stock to get a little more zip from each gear and still have a nice overdrive-ish 6th gear.
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