I have an Optiplex 7060 with the Foxconn PVA080F12H fan with a fairly ordinary 4-pin plug, as opposed to Dell's often-seen 5-pin plug (one empty).  Here's a photo:

This looks a lot like the pin-out for 4-pin Standard ATX Architecture fans; my presumptions are:

red & black are +12V and GND,
yellow is RPM feedback,
blue is PWM signal.

My hope is that I can replace the rather inadequate OEM fan with something that can push more air, much more than the stock 45 CF/M fan. 

I am cautious about this, since Dell is famous for defying ATX standards with regard to color codes.  Any recommendations?