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...