https://www.cnbc.com/2018/01/09/microsoft-says-meltdown-and-spectre-fixes-will-slow-some-pcs-down-significantly.html

Microsoft on Tuesday provided new details on the performance impact of updates to protect against recently disclosed security vulnerabilities. In certain cases, performance on Windows will be significantly slowed by patches for the Meltdown and Spectre vulnerabilities.

Some people have found that that their servers and PCs are performing differently after installing updates, so the news shouldn't come as a big surprise. Still, the new information doesn't line up perfectly well with what Intel said last week when the vulnerabilities were first officially announced. "Any performance impacts are workload-dependent, and, for the average computer user, should not be significant," the chipmaker said.