Supercharger cables are cooled and there is now way for the extension cables to be.
Since our vehicles are limited to 97kw, I think the extension cable will be fine. I plan on getting one as soon as they are available.
Remember, it's not just that the GV60 will take up two spots at a v3 station, possibly annoying other drivers. More importantly, YOU won't be able to charge AT ALL unless two consecutive spots are available. At many Tesla stations around here you might wait quite a while for 2 consecutive spots to open up. Maybe just go to an EA station instead.
Here's a handy tip - in the Tesla app, look for stations that say 325kw (instead of 250kw). That's an easy way to tell that a station has v4 dispensers with the longer cables, so that only one spot is needed. Even though there are many more stations with v3 dispensers than v4, there are still more Tesla v4 stations than there are EA stations, at least here in California. That said, I've managed to make my two most recent road trips using only EA stations - one trip from LA to Vegas and back, and another from LA to the Monterey area and back. But it definitely reduced my stress level knowing that I had the option to use Telsa stations if necessary.
On my recent trip I made an overnight stop in San Luis Obispo, and made sure to stay at a hotel with 9 Tesla destination chargers. These chargers are not free (you have to use the Tesla app to pay), but they do include the adapter for J1772 so I didn't need the one on my trunk. About an hour before arriving I checked the Tesla app and confirmed that 8 of 9 were available - perfect, or so I thought. When I arrived I found out that all but one was ICE'd!!!

I was very fortunate that there was one available. I can't really blame the drivers, because there wasn't even a sign that said parking was for EV charging only. I don't think that ICE drivers should be required to recognize what a Tesla wall charger is. I complained to the hotel about it when I left -- what is the point of having EV chargers if they aren't going to be available?? By the way, the reason why the Tesla app didn't say that 9 of 9 were available was because one of the chargers didn't have the plug properly docked in the unit - in fact it couldn't be docked because someone had made off with the J1772 adapter. So the Tesla app thought it was in use. Not sure if I'll stay in that hotel again, or if I do, make sure I get there early before all the stalls are ICEd. It sure was nice to leave in the morning with 100%, which allowed me to complete my trip without having to stop at a fast charger.