Giving a box to tick inside the setting menu to be switched on or off to show each players polygon count that refreshes in real time or each time they change avatar sounds like a nice implementation.

eg. above/below the name tag

As this would allow users to be able to select a certain users and not show their avatars to get a more versatility when it comes to filtering performance gain. And this would also allow users to identify who is using a modified SDK to upload more than the limit polygons.