Ok, some calculations:
Diameter: 695,4 mm (27,4")
Diameter: 658,6 mm (25,9")
Difference of 36,8 mm (1,45")
that means the ride height wil drop with half the difference: 18,4 mm (0,72")
To me that sounds like almost no difference at all. The tire width however is increased with 22%!
Going from the 90/90-21 to a Supermoto 120/70-17, the front axle will drop by 47,8 mm (1,88") that a bit more.
All in all, i'm very positive about the difference. I will confirm that with the standard skinny tires, even with dual-purpose tires, on dry pavement, you can really ride hard on the road. However, throw in some cold, winter weather, rain, etc. and those ties can become a bit iffy. And i have had the front slip a few times. None of that with the current wheels and tires, so far. Perhaps the looks are nicer with the wider tires, but have you seen my bike, I don't really care about appearance. I'm function over form.
Anyway, who else has some positive stories about these wheels?
Suzuki DR 650 SE 2006