can you tell me why you changed them? to me it seems that the gearing is a bit low - 1000 rpm in 6th gives 20kmph. I think i would rather get to 25kmph. you can always drop a gear
i am considering changing the sproket to effectively give me a 7th gear. i use kmph not mph 5000 rpm is 100kmph but id rater it was more like 125 kmph dont have to change gear so much