ecpm differences between ad networks and between banner and popunder
 

Can anyone with real experience answer these two questions:

1. Does ecpm for banner ads vary significantly between ad networks?

2. Given some number of uniques per day, roughly how much more revenue can I generate (by percent) if I use popunders instead of banners.

Obviously I am looking for ballpark estimates but if you have specific numbers that would be great too. This is for a tube indexer like nudevista.