Ask YC: Scheme vs Common Lisp - power/expressivity comparison.

I would like to read your opinions about the comparison of power and expressivity of Scheme and Common Lisp. I currently only know Scheme, and I want to decide if I should spend more time and effort on this route, or if it is worth learning Common Lisp for me.

Specifically, I want to understand if there is anything that can be done in Common Lisp that can't be reasonably easily be expressed using a present-day Scheme system.

One thing I read somewhere is that reader macros (which I don't grasp yet) are such a thing.

Other thing would be low level macros - but there are Scheme systems that allow you to use define-macro and gensym (non-hygienic macros). Is this (even if more cumbersome) as powerful as the Common Lisp counterpart?

Finally, Common Lisp has dynamic scope - but to me it looks like everything that can be done using this could be done using macros that capture variables (which some Scheme systems also support). Am I wrong?