If you have designed more than one web page for split testing, below are some points which would help you measuring overall success and effectiveness of each layout and you will have more confident on deciding perfect design which promise of good conversion.

Percentage of successful conversion: You can measure the total no. of conversion for which you have designed the page whether it is purpose of sign up, news letter subscription, quick contact or product purchase. 
Percentage of bounce rate in different design: If one layout has remarkable difference in bounce rate, you should try to analyze the parameter and can select the one with lower rate. 

Average time on site of your visitors: Once visitor lands on your website, how much time it takes to navigate through other pages of your website. You can select the design with higher average time on site. 

Percentage of clicking on specific elements: if you want to lead your visitors to specific page, you can display same page URL as image link and text link in two different versions and can measure percentage of clicks between them.

Abandoned paths in conversion: If the final conversion requires intermediate steps, you can measure the percentage of abandon rate in different version and at the path or intermediate step, where they have abandoned. For example If  the final purpose is the purchase of products, which require three steps, registration, credit card process and confirming final payment. You can check the percentage of visitors who left without purchasing the product and can also measure the steps where they have left your website like after registration, at payment time or in confirmation.