Website Optimizer adds a new feature “auto-disabling” which automatically prune poor performing variations. This keeps overall conversion rate high while testing. Additionally, by removing poor variations automatically, your traffic is focused on only the variations that have a chance at winning, which means experiments should complete faster. Auto-disabling is available for any Website Optimizer experiment with more than two variations (i.e. you can't use it for an A/B test, but you could for an A/B/C test). You can enable it from the experiment settings page.