Windows 8.1 Preview does come with lots of improvements, but the first Windows 8 overhaul also removes some traditional and popular features, including the Windows Experience Index.
Introduced in Windows Vista, the Experience Index was used to determine computer performance, including hard disk speed, RAM, CPU, gaming performance, and video capabilities of a specific system.
Just like McAkins Online points out, the feature is completely missing from Windows 8.1 Preview and until now, no workaround has been found to bring it back.
It’s not yet clear if Microsoft plans to bring it back in the final version of Windows 8.1, but more details will most likely be provided at a later date.
Given the fact that the feature was already available in Windows 8, expect at least a similar performance measurement tool to be introduced in Windows 8.1 RTM.