A 13% conversion rate puts you in some pretty good company.

Check this thread:

http://www.zen-cart.com/forum/showthread.php?t=106934


I would have to question the numbers at the end, though. 53% click the Confirm Checkout button, and only 13% actually pay at PayPal? Doesn't seem right, unless they're seeing something they don't like at PayPal's site. Have you tested the process yourself?