Forget those 2 instances. There IS a way to force Linpack use more threads than number of physical cores in a system from within a single process. If only I discovered this earlier...

Intel suggests using only physical cores probably because of P4 Hyperthreading which does perform worse in Linpack (not only there ) when turned on. Why is Intel so secretive anyway? There is no mention about threading control in Linpack's documentation. Google is a real life-saver.