using google adwords keyword tool if a keyword gets 100,000 searches per month and you have the top spot on the google search for that keyword how much traffic can you expect per month or per day? is there a consistent percentage number that can be attributed to the top position on google searches for particular keyword term ?
There is no guaranteed way you can know what top spot in Google will achieve, however, try using the Google Traffic Estimator tool, it should give you an indication. Put $100 for CPC, change the settings to the location, and you should be good to go..
Check this out: http://training.seobook.com/google-ranking-value Should answer your question and then some; just make sure to remember to optimize title tags and the meta description not only for search engines but also humans!
Is bringing in the traffic your only concern? Having the top position is very important, but I think you should also put emphasis on the goal of having the site on top, like getting more leads etc.
First of all, you want to make sure you are looking at the exact match search volume, not the broad match. This will give you a more realistic idea of what the monthly search volume is. Then, you can estimate that 42% of people are going to click on the first link in Google. This percentage may or may not be exactly accurate as it was from leaked AOL data a while ago, however it should give you an estimate. Hope this helps!