Conversely, I went to a 16t front (gen Suzuki) and wouldn't go back to stock.
Motorway jaunts have the bike lower revving and feeling a bit less frantic, yet there's still plenty of get up and go in top cruising at 80. Obviously you get slightly reduced performance in each gear than you would with stock gearing but nothing that bothered me (as with anything, if you want more performance use more revs and a lower gear)
As GW say's, the speedo will read pretty accurately with 16t front, the odo will log a few % less mileage which also has a corresponding reduction of the displayed mpg - although actual mpg is pretty similar between the two gear ratios. Add about 4mpg to the dispalyed figure is reasonably accurate.
I generally go for DID X ring chains , along with genuine front and 'any brand' steel rear sprocket, which begs the question why you want to go for a less durable alloy rear?
An oe kit is the easy option, aftermarket kit the cheaper, easy option. A gen sprocket, did chain + whatever rear probably the expensive option to be honest, I'm not too impressed with the oe chain used by Suzuki.
Horses for courses, as ever its down to personal choice,
