It depends on what you talk about with "performance". Some years ago, Allegro had the faster GC than SBCL, but SBCL certainly had the best code generator of the three Lisps. So unless your runtime is constrained by the GC, SBCL really shines for performance. And it gives you a lot of knobs to optimize the memory usage.

SBCL generates the best code for toy benchmarks and number crunching applications. Throw it against a CLOS heavy codebase and you'll be surprised at how it runs VS Clozure CL and the aforementioned implementations.

ACL's GC is still the best hands down (and of course ABCL by virtue of the JVM). I think SBCL is still sporting a conservative GC on x86.

Not sure what you meant by "toy benchmarks", but to me this has a very negative connotation. The SBCL compiler excells at complex code and regularly produces much better output than most Lisp compilers. CLOS is a very bad example for judging the compiler quality, because its performance heavily depends on the implementation. To compare compilers, you would have to use the identical underlying CLOS implementation. A bad one can ruin your performance independantly of the compiler used. To make comparisons, one needs benchmarks where the whole code in question is compiled by the different compilers.

To my knowledge, SBCL switched to a precise GC some time ago. But I still would expect ACL's GC to outperform the SBCL one.