Cheers for measuring yours, really appreciate it :)! Appreciate what you say around a multimeter using averages but it does look as though our numbers are pretty similar, it is weird that I still get an undervolt.
Also tried something else this morning, I wondered if my pi was particularly sensitive to voltage so I tried another one I have which behaved exactly the same way so that rules that out. Good to know you are using the supplied USB cable for pi to Picade, I'm now thinking the problem could lie in the USBs I am using for atxraspi to pi not providing enough power. So I'm on the hunt for the shortest best power rated usb a to micro cables. Any suggestions :)?
I don't think I've got any dry joints on my atxraspi usb output, here's a photo, what do you think?:
Just out of interest, there were 4 small pins under the usb out but only + and - labelled on the outside of the four on the pcb. Did you solder all 4 joints like me!