Changing Sprocket Gearing

I'm looking at going to a 15/45 (-1/+2) setup on my 6R, but I'd like to get some opinions on a couple of things first. 
Steel or Hard Anodised Aluminium rear sprocket? As with tyres, I don't mind sacrificing a bit of longevity to get a bit more out of it (From a performance perspective) but I don't want to be replacing them every 1000kms.
Any brands that should be avoided, or are they all pretty much on par with each other?
In regards to speedo calibrators, is it worth getting something flashy like HealTech's SpeedoHealer? Or is something simple like the SpeedoDRD just as good?
And lastly, is factory speedo error fairly uniform across bikes of the same model? (I.e '08 ZX6R #1, '08 ZX6R #2 etc).
It's all a little new to me as I never fiddled with sprocket gearing (Or much else aside from basic maintenance) on my 250's.
Cheers!

Steel or Hard Anodised Aluminium rear sprocket? As with tyres, I don't mind sacrificing a bit of longevity to get a bit more out of it (From a performance perspective) but I don't want to be replacing them every 1000kms.

Any brands that should be avoided, or are they all pretty much on par with each other?
In regards to speedo calibrators, is it worth getting something flashy like HealTech's SpeedoHealer? Or is something simple like the SpeedoDRD just as good?
And lastly, is factory speedo error fairly uniform across bikes of the same model? (I.e '08 ZX6R #1, '08 ZX6R #2 etc).
It's all a little new to me as I never fiddled with sprocket gearing (Or much else aside from basic maintenance) on my 250's.

Cheers!
