I am using the nginx you pointed to, the latest version. It seems to be running 9 instances in total, my CPU is a quad core with hyper-threading (intel e3-1230v2, with 8 worker processes running (didn't go above my theoretical core count)
that is with 10 php instances open, set up with the 9001 - 9010 port switch
that is with 10 php instances open, set up with the 9001 - 9010 port switch