Many online businesses consider visitor engagement as an indicator of success.
Does something about Experience B's creative resonate with visitors so they consume more (or more valuable) content than Experience A? Capture information about your site visitors and measure their level of engagement with statistical confidence. You can choose to capture engagement when selecting your success metrics. This means that "success" for a campaign does not have to be simply reaching a particular place on the site or performing a particular action. A visitor's aggregate actions can be used to measure success.