I've used the CL package in Emacs (with the proviso that if you're using it to build an Emacs library, as I was, then you're supposed to restrict its use to compile time, which is weird and takes back most of the value). It doesn't make Emacs Lisp into anything much like Common Lisp. The two are very different languages. The CL extensions in Emacs are kind of useful if you already know CL, but they're also a strap-on and the result is predictably a monstrosity.
I think you'd be better off picking which of the two languages you're interested in and learning that.
I think you'd be better off picking which of the two languages you're interested in and learning that.