"The upshot is that computer owners upgrading to Windows 10 from Windows 8 (and presumably Windows 7) should expect to get the same level of performance out of their machines that they do now, and should also expect to make the transition smoothly, without losing access to data, files, applications or otherwise crippling their PCs.Windows 10 tested: How performance on the new operating system compares to Windows 8 - CNET
In previous Windows OS cycles, this was not always the case, and our recommendation in the past has been to wait until you buy a new computer to get the newest version of Windows. For Windows 10, based on our testing to date, that caveat is no longer required."
Thursday, July 30, 2015
Windows 10 tested: How performance on the new operating system compares to Windows 8 - CNET
Final paragraphs of yet another better living through lowered expectations Windows 10 review