BTW, 1min 5min 15 min are the load average .04 1.20 2.30 representations you see in top or uptime ... So, the answer is "how long is a rope?"

The more CPU's or CPU cores that you have the higher load you can tolerate ...

Interesting reading, see: http://www.linuxjournal.com/article/9001 and
http://overclockedtech.com/?p=257