The OS is 64bit Gentoo Linux and the Perl is 5.8.8. But nevertheless I had the/my Perl-Interpreter under suspicion because it's compiled with GCC 4.3.1 -march=core2.

Unfortunately it behaved so well on all machines, that there is no "conservative" perl left as reference. My bad. As also all testcases of Perl ran OK, this could be a candidate for a testcase. Or even a new class of tests (expected memory consumption). Maybe this could be carried to perl-porters