Best mesh extender for Model R8000P ac4000 tri band night hawk router

What is best performing mesh extender for my model R8000P night hawk x6s ac4000 tri-band Wi-Fi router. I want to buy highest performing net gear mesh extender for that router. I'm not very technical but if router has a maximum speed it does not seem to make sense to buy mesh extender faster than what router can support. If someone can point me to the fastest mesh extender that makes sense for that router I would greatly any feedback.