I haven't noticed it to be slower, but I'd accept slower for the privacy benefits.

I have noticed it to be slower, and with more broken websites. I still prefer it over chrome.

I don't know about others but when I click youtube links on reddit the back button is disabled. Not sure if it's a bug or by design but I don't remember it always being that way.

It depends. For work related stuff I will always choose speed and responsiveness.