On a B6, the effect of going one tooth down is that, accelaration is much improved. Your get to your desired speed faster. It actually makes a B6 get up and go.
Of all the mods I've put into my B6, this is probably the most bang for the buck one. The 14T countershaft sprocket only costs ~$16, and about three hours of my time. The hardest part was breaking the countershaft sprocket free. I don't quite remember, but I think it was 125ft-lbs?
The down side is that the vibes are higher at all ranges, so you need to counter act it at the handlebars by dampening the vibes (Barsnake and/or gel grips). Also you loose your maximum top end speed.