If you are direct linking then this is a more complicated answer, however if you are using your own landing pages and encoding them with Prosper202 landing page javascript code then you can use the full power of P202 to see which landing pages ultimately have the best conversion rate, from beginning to end. HINT: Click on Analyze and then Landing Pages.
If however you ARE direct linking, and dont control the landing pages, you'll need to make sure you are using P202 as the tool which is doing the landing page rotation. Then you can go to the Visitors tab, Display only Show Converted Clicks and count the amount of times you see each landing page when hovering over the Redirect icon for each Subid. Then its just a matter of doing the math.