AMD isn't catching up in the server CPU world, they surpassed Intel a while ago., as far as performance, efficiency and density is concerned. What's held them back is that you can't integrate an AMD host in to a VMWare host cluster that's running Intel CPU's. High Availability doesn't work and VM's cannot migrate from one CPU platform to the other. Integration of AMD hosts has been slow because of that. For those replacing hardware, yes, a lot of providers have gone to or are going to AMD for the, cost, efficiency and density.
As far as this threat is concerned AMD platforms are already running the code necessary to mitigate it. No update needed. So any realized performance losses were in place from day one. It's impossible to say what those losses are since there is no control to compare to.