.stl files as loaded by the 3D extension are currently served without compression, which roughly doubles their size versus applying gzip at the HTTP(S) layer.
https://upload.wikimedia.org/wikipedia/commons/a/af/Asad_Al-Lat.stl
1,470,284 bytes raw -> 700,075 bytes gzipped
https://upload.wikimedia.org/wikipedia/commons/0/0e/Venus_%28Afrodite%29_fra_Milo_-_KAS434_1.stl
137,129,384 bytes raw -> 67,906,901 bytes gzipped
as tested with gzip -9