I put a Vortex -1 front sprocket on my R6 and I noticed quite a bit of difference. Not major, but it is noticeable. Also, I didn't have to replace the stock chain...all good there. Dropping one tooth on the front sprocket is the same as going +3 in the rear.
As was said, however, the more teeth you have on the rear, the more torque you are going to have. I am currently building a stunt bike (02 F4i) and one of the first things that I am doing is going +7 rear and -1 front (works out to the same as +10 rear).
As I am sure you are aware, however, you are going to loose top end speed. What I have seen is that you loose about 10% on top with a +5 and 20% with +10.
Hope that helps...