In fairness, "SIMD support" is not exactly "the compiler can reduce code to AVX instructions" but more like "you can now write non-portable custom assembly-like code to make your code faster".
That's what I mean by "willing to hack"! Getting the compiler to use SIMD instructions is actually pretty easy- you just specify where to use them and let it handle them. Then you pinky promise that your array really is made of floats and turn safety off.
Yup. I used to use Clozure CL all the time, but since the code I write tends to involve lots of number crunching, SB-SIMD and Loopus are indispensible.
Even before SB-SIMD, SBCL has always seemed like the best Common Lisp implementation for any arithmetic. Or at least this seems to be case when you benchmark CCL against it :)