Ur talking about the present, getting low fps right now. I'm sooo sorry I didn't read your mind, and that I didn't add the word 'yet', and was trying to help, because it baffles me how you've not reverted yet knowing you have this issue.
You don't know if the fps lag will be there in the future. U still have a week to use the old client, and possibly more, as there are some rumours for a workaround for using the old client longer. And they have a week for fixing performance issues, as many are crying about it, not just you.
On a side note, I'm not your enemy. I think it's bs that they're shipping it so fast with so many issues at large, and with the biggest one, like I said in my opinion - losing LP cus of client crashing -, not being on their priority or 'well-known issues' list.