Slackware :: Severe Performance Degradation In 13.37 - Taking 2 To 3 Times Longer

we bought a dual 12-core Opteron machine (Supermicro H8DGi board). Installed Slackware 13.37 and performed some few tests. We observed that performance quickly degraded as the box became loaded. For instance, a lonely task may took "t", but when running 24 of them at the same time (fully loaded box), it may took 2 to 3 times longer. From some test we did (tinkering with BIOS, moving memory modules, etc) we came to the conclusion the problem was due to a terrible memory managment. Finally we solved the problem by recompiling the kernel and taking the .config file from OpenSuse. Thus, there must be something to be tweaked in the standard Slackware .config file