Phoronix have done some benchmarking on the Linux patches, using a Haswell processor (released 2013-4).
https://www.phoronix.com/scan.php?page=article&item=linux-kpti-pcid&num=1
It looks like for the average users day to day use on recent PCs, including gaming, the performance hit will be minor at worst. I have absolutely no reason to believe that any MS or Apple OS patches will be different.
Now all I need is a benchmark for Penryn processors from 2008.
