[gigamonkey]

Last I knew, CLISP was based on a bytecode VM while SBCL and Clozure generate machine code. I think there may be some work on adding a JIT to CLISP but as far as I know it's still experimental.

[apgwoz]

That would probably explain it. Seems like it might be a good use for GNU Lightning.

[mahmud]

CLISP uses GNU Lightning in some superficial sense, but it's a compile-time option not normally built into release binaries.