If you're using the same compiler and same optimization setting and same CPU architecture on both systems (e.g., gcc), then I'm surprised.

Yes - my feeling, too. I did wonder whether perhaps the linux perls had been built with -Duselongdouble (it's certain that the Windows perls weren't). But that's not very likely, and I can't see how the optimisation level would play a part even if the linux perls *had* been built with -Duselongdouble.

Still, I thought I'd mention this in the off-chance that it's relevant ....

Cheers,
Rob