I just saw the warowl video of new cache he goes from ~500 to ~300 fps. I don't think it's a shitty GPU. It's just the old source engine mixed with a lot of detail which it doesn't handle well.
I can tank the FPS of any modern PC with a modded out version of Morrowind. It still looks like crap but the engine wasn't built to support such level of detail so it tanks the performance.