I know I switched because it does everything Sublime Text 2 does for me - and then more. I even created my own package and published it online because it was so intuitive to extend.
Its def slower. I do like atom, however I tend to end up doing a lot of heavy log crunching. Atom will stutter and crash whereas sublime breezes through anything I can throw at it.
It seems to be slower than ST, but I didn't use it enough to see if it really is slower than ST in a all day work.
I read somewhere that there is a beta release now, I'll upgrade and give it a try again.