OK, I didn't have a Pro 5, but I did have a Pro 4 (long story below*). It had a different headstock shape as shown in the photos already here, gold hardware, and a Mighty Mite pre-amp with a volume control for each PUP (still the EMGs) along with a bass and a treble boost/cut control. The real difference is that the Pro had a maple body instead of the poplar of the standard series.
I didn't much care for the pre so I yanked it out of mine and replaced the controls so I had a master volume, a master treble cut (passive), and a blend pot. The fourth hole was just a dummy pot to hold the knob on.
*I ordered a Pilot from the store I used to manage. About six weeks later the sales rep asked how I liked it, and the owner said it hadn't shown up yet. Turns out it had shipped right away but UPS drove a truck over it at the first stop after it left Westerly. They just convenienlty "forgot" to let Guild know. The problem was that they'd discontinued the series and the one UPS trashed was the last Pilot. So we had to wait for them to re-tool for the new version. And my bass went to NAMM where Ernie Ball/Music Man asked them to change the headstock as it was a 3/1 arrangement. So, then Guild went back to redesign the neck and re-tool. As a result of all the protracted delays, they sent me the Pro version instead of the regular version I'd ordered, and they didn't charge my dealer the upcharge.
I eventually sold my Pro to a former student of mine, and have recently been wondering if Jeff still has it...
jte