Although XP was "EOLed" some time ago, MS DID release a version of the WannaCry protection update for it. (I installed it into all of our machines ASAP with no issues.) I suspect that, due to the huge scope of THIS vulnerability, they just might do that again... seeing as they still have some limited security update support for XP that is used in Point of Sale systems, etc, by the millions.
If the performance "hit" is 5% or less, then that's fine, and probably not even noticeable. 30% would be VERY noticeable.
Eyes open and fingers crossed, as they say. ;)