Earlier quoted context omitted.
What do you mean by that? A lot of people use racket, a lot of people use SBCL, which is indeed significantly faster. They are actually completely different software for different purposes and very different strengths.
what are strengths of sbcl over racket? what are strengths of racket over sbcl? if sbcl raw speed > racket speed wouldn't most expert lispers by default choose sbcl? what purposes does racket uniquely serve not served by sbcl?
SBCL is a Common Lisp implementation, racket implements variants of Scheme. SBCL is natively compiled, creates standalone executables.
> what are strengths of racket over sbcl?
It implements various scheme dialects, the ability to integrate different languages in one image is unique. It offers an integrated enviroment with a lot of libraries included, that is why it is popular in academia.
> if sbcl raw speed > racket speed wouldn't most expert lispers by default choose sbcl?
First of all, they implement different programming languages, that means they are not competing directly with each other and are very different beasts as discribed above. Racket seems to be very popular in academia, while SBCL is more used for practical software development. At least that is the impression I have.
> what purposes does racket uniquely serve not served by sbcl?
I think I have answered that above.