[Shiunbird]

This is something I actually would love to ask a microprocessor designer...

I understand that a single core can run two threads - however, I also understand (hopefully rightly) that the efficiency with which a single core can run two threads will depend on what tasks these threads are running.

AFAIK some of the newest IBM power cpus can do 4 threads in a single core - I just have no idea how and what the tradeoffs are.

So... way beyond my knowledge.