I'd try running check disk to rule out any bad sectors that might be contributing to the slow down. Disk Check
You could also go to the hard drive websites to see if they have any specific diagnostic tools to troubleshoot/check disk performance. Personally, if your machine is working as expected and WEI is the only issue you're having, I wouldn't sweat it. As Microsoft says:
Each hardware component receives an individual subscore. Your computer's base score is determined by the lowest subscore. For example, if the lowest subscore of an individual hardware component is 2.6, then the base score is 2.6. The base score is not an average of the combined subscores.
To me, that's not a realistic assessment and not something I'd worry about. Maybe my machine can't have it's GPU upgraded and that part scores a 2.6 but everything else is in the high sixes. Just my 2 cents worth.