I have the 5300. I believe Gonks (and mine) are identical with the 5300 adding a voltmeter. I normally never take the time to observe the voltmeter and it adds to the light pollution of power button indicators (does include a dimmer with an off setting) so if you are interested in either model I would take the savings and purchase the 5100. When I purchased my unit the 5100 was out of stock. Otherwise same unit I believe and rated 7090 on joule.

My powered SW and 770 are both plugged into the panamax via the two delayed-on outlets for high-current components

The 5500 is at 2025j but almost double cost of 5300. There are cheaper ways to achieve a higher rating for surge. Clamping speed is something you should pay attention to and If memory serves I noticed it was faster on the Series Mode based protectors. Another reason I became interested in them, while I was checking it all out. There really are cheaper ways to do it than via the Monster Pwer/Panamax route. When I was pulling up surge protectors for my main panel on the web, I believe some ran 29.00???

Where the Panamax pleases me the most is during delayed startup if it senses under/over voltage, Its not perfect but I have heard the whole house going off in chirps and beeps when the power company is trying to re-initiate the line. The power might hit the house 3 times (on/off) in rapid succession till it stabilizes and finally remains on.
During this time often (not always) the panamax (I guess depending on the level it senses) will remain off.
Which spares my AV this rapid on/off sequencing.

Edit: I typed same time as but check the series mode, I believe they are faster reaction. (And those are hard spec to run into but if you dig on the web I know I’ve seen some info on that topic. A “Brickwall” link is posted under 950 forum no sound after power outage. That was one unit I “would” have purchased over my Panamax at the time but back then Brickwall did not have all-inclusive unit which covered the coxial lines….I needed a quick fix for all at that time.