Sprocket and gearing was a very difficult concept for me to master. I have a torque converter and when trying to work out overall gear ratios, I had to learn how to take it into account. Once learning the maths and working out all the ratios... I decided to buy a 71 tooth sprocket.

I'm running standard 11" go kart slicks. a 71 tooth is the absolute biggest I feel comfortable getting based on this wheels size... any bigger... and I would be too concerned with the sprocket and chain hitting the pavement.
Initially I purchased a much smaller sprocket (55 tooth) thinking that the smaller the sprocket the overall higher the speed.... this is kinda true... however what I didn't realise was it also requires more torque. As a result the go kart took off "REALLY" slowly and struggled to get to the high speed because of the lack of torque
Next...
I bought a bigger sprocket (64 tooth not going too big) to try and find faster acceleration, and sacrificing the top speed (which I could never get to with the smaller sprocket)... Acceleration was much better and top speed was good too.. however I really wanted to take off much faster.
Then...
I settled on a 71 tooth... BAM! Now with such a huge sprocket it really takes off like a rocket... "almost" keeping up with two strokes... (not a lie). It's like a new kart and now that less torque is required to more the sprocket.... the engine finds it easier to get to the higher Revs and top speed is not the issue I thought it would be.... Also keeping in mind that on a race track most of the speed is needed around the corners.... I don't even think my kart gets to its top speed on the track we go to. This sprocket clears the ground by about 25mm... so the track needs to be really flat.
Moral of the story.... don't waste money on heaps of sprockets unless you have different conditions.... Get the biggest you can...
Lastly the quality of the sprockets are great. They fit the sprocket holder perfectly, holes line up perfectly. I'm very happy with my final choice.