So how much of a difference do these make on top speed? Seems like the 9 tooth would be nice for getting a little extra torque for every day driving, assuming the top speed is still good (which I would assume yes)
For all practical purposes, on a reasonably geared cassette and normal powered chengine you probably won't lose any top end with a 9 tooth...maybe 1 mph or something.
With an 11 you can expect some better top end speed, if your engine is putting out some power.
When I run these gears, it shifts (so to speak) the whole ratio set.....let me be extreme: I have run an 8 and I have run a 12. We did not bring these to the market because the entire ratio shift is too extreme . On the 8, while it is a torque monster, it really runs the low gears together. 1st and 2nd are so low there simply in no difference felt, and taking off in 3rd on the street is fine. From 0-20 mph, all gears on a 6 speed have been run through. With the 12, I can't take off in 1st unless I do clutch tricks, and high doesn't do well with a 2 stroke chengine - it would be VERY high top speed IF I had the engine of the Gods.