I agree with the lexical scoping part (explains more or less why I don't use Lush). Its a pity that there aren't any good numerical computing tools in Common Lisp/Scheme. Oh, well.
In contrast, SBCL uses tagless float arrays, so that array operations tend to be cache friendly. With adequate declarations, numerical code in SBCL tends to very fast (~1-3x C speed). I assume one can do the same with Bigloo and Chicken scheme as well.
http://lists.racket-lang.org/users/archive/2013-April/057487...
This is also the case in Racket.
http://docs.racket-lang.org/reference/flonums.html#%28part._...