Google has created a way to do a controlled AB experiment with Miva Merchant.
You can use Google website optimizer to compare the same website page displayed two different ways to see which one performs better statistically. The following link gives step by step instructions with a great example of a real world scenario with Miva Merchant. If you are confused just watch the short video tutorial and it will make perfect sense.
http://websiteoptimizer.blogspot.com/2009/03/test-your-add-to-cart-button-in.html