I played with the latest version of Cyberfox x64 a week or two ago. It was very quick on my i7, although I didn't install all my extensions to see how much speed would suffer.
I'm still debating on whether or not to switch from Pale Moon. Pale Moon's author is very transparent about what differences are between it & Firefox plus there's an excellent support forum. Cyberfox's list of differences is just some vague wording on their home page.
Yes, I posted on Pale Moon forum some time back. The author is right onto issues. It is my understanding that Pale Moon is a different implementation derived from Firefox. Cyberfox is basically just another build using optimizing 64 bit compilers. There may be a bit more than that to it. But you see Cyberfox match the Firefox version within hours. So it must be a few compiler compatibility tweaks and build it.
I don't load Cyberfox heavily with Tabs. I rarely have more than 8 open. Also the AddOns I use are not heavy duty. Mostly stuff like Lazarus, font size changer, classic theme restore etc..
I was using 32 bit FF for a few weeks because Cyberfox got a bit weird. It seems now even the update checker in the About Box is working again. I can't tell it from FF 32 bit. Even load times seem the same. I think the AddOns are almost identical. I use Super Start for speed dial.