http://www.pcgamer.com/intel-shares-more-benchmarks-including-graphics-from-spectre-and-meltdown-patches/

Intel has provided an expanded set of benchmarks that compare the performance of several generations of processors before and after applying Meltdown and Spectre security patches. In doing so, Intel stands by its previous claim that users can generally expect a six percent performance penalty or less, though in some cases the numbers show it could be much higher.

The most alarming benchmark result from Intel's own numbers is a 21 percent hit on a Core i7-6700K processor, which was also paired with an SSD in Windows 10. It stands out as the biggest penalty of the bunch, though to be fair, it happened in an individual test in Sysmark 2014 SE—the overall drop in that benchmark checks in at eight percent.