The most performance impacts will be older WIN7 devices as documented below: 

https://redmondmag.com/articles/2018/01/09/microsoft-meltdown-spectre-slowdown.aspx

https://cloudblogs.microsoft.com/microsoftsecure/2018/01/09/understanding-the-performance-impact-of-spectre-and-meltdown-mitigations-on-windows-systems/

Performance slowdowns will be most apparent for older Windows client systems, such as Windows 7 and Windows 8, particularly when using Intel Haswell chips on “2015-era PCs,” according to an announcement by Terry Myerson, executive vice president of the Windows and Devices Group. Microsoft expects “most users to notice a decrease in system performance” on these older Windows clients.