Oh my god, what a dumb dumb I am. Penny has dropped.
Now getting 184pps from a cheap dual-core G2020 ivy bridge, using original unmodified sourcecode. Pps still fluctuates though.
Ahh, can't believe it's take me over 2 days to realise what I had to do to double the pps. Kicking myself.
Now let's see if it works on EC2...
Useless post if you don't tell us what you did. You may as well have mumbled it to yourself.