That said, I’ve seen usability studies that say the number 1 ranked site gets clicked about 35% of the time, down to the #10 ranked site being clicked 2-5% of the time.
Interesting. It will also depend on the quality of your competitor´s sites. If you are competing for a deserted market like underwater basket weaving and the top spot is the only site that has real content whereas the other 9 only have superficial forum questions, your click through rate will increase exponentially.
As has been mentioned, estimating the volume of keyword traffic is probably impossible or near impossible at best.