Profit by Impression : The real metric in PPC testing
Profit by impression (PBI) and Profit by Click (PBC) are the best metrics to determine when split testing ad copy or landing pages. One can determine profit by impression/click numbers by individual line of an ad copy, by the entire ad copy, by landing page, etc.
When split testing, think about the actual goal: sales. By understanding how each line of an ad interacts with a landing page and with a search query, by understanding how a landing page is affected by a keyword, by understanding how a keyword interacts with a specific ad, by understanding all of your metrics you can finally determine which is the proper combination to be running.