The average for SERP CTR for the #1 position is approximately 23%. Sorry, Delco your numbers are way off. Those numbers are from the leaked AOL data and if you look closely you will notice those numbers are percentages of clicks, not click-through rates, there is a big difference between those two.
Also, you should note that while 23% is the average SERP CTR for position #1 it can vary wildly from one keyword to the next. And it can vary a great deal based on how compelling your page title and description snippets are written.
So in your example keyword of 50,000 searches, you would need to be ranked #1 to have a chance of getting 5,000 visits, just reaching the 1st page would likely only get you 500-1500 visits if you are not in the top 3.
Don’t expect anyone to post actual CTRs for AdSense as it is a violation of the TOS to do so. I would say that 90% is unusually high and that 0.9% is unusually low, but it can vary that much based on different topics and placement of ad units. How well targeted your traffic is also has a great deal to do with your AdSense CTR as well.