Normally when we show a comparison video like this, it's comparing the same game across platforms. But this one's different. It's two games across two platforms, which may sound pointless, but remember, these are driving games we're talking about. We can get away with it.
Moto Games TV found that both GT6 and PC graphics showcase Project CARS both have the same track (Monza) and the same car (Pagani Huayra) available. So they took both for a spin and recorded the results.
You should probably watch it in 1080p for the best results.
While it's easiest to say "Oh, Project CARS looks better, especially inside the car", that's missing the point. That game is running on a modern PC. Gran Turismo 6 is running on hardware released in 2006.
Gran Turismo 6 vs Project CARS Build 623 - Pagani Huayra at Monza [Moto Games TV]