Erm you have to look at the entire funnel and not just a banner CPC. You can pay a very low CPC and get shitty traffic that does not convert or vice verse.
You have to measure from the start of the funnel (usually the banner) to the end (the lead/sale) and see where you can optimize your media buying.
For example:
If all your visitors bounce, there is something wrong with your landing page. This can be anything from slow loading speeds to people know knowing wtf they are supposed to do there or because you advertised a penis pill in the banner and the landing page is selling big titty tranny midgets.
So it's a hard question to answer w.o. knowing what exactly you are doing - a good zone will send you the right traffic for the right price, so you have to be able to calculate your ROI for each media buy - if you can't do that, you are just shooting blind. You might hit but you are probably just wasting ammo.
