There are probably less than a dozen PS3 games that actually render at 1080p or some facsimile thereof. Gran Turismo games are 4 of them. Wipeout HD and Ridge Racer 7 are two more. I doubt any multiplatform games do regardless of what the boxes say.
Honestly, you're actually proving my point with how badly optimized Gran Turismo 6 was, like how you said that the PS3 couldn't possibly keep up with those kinds of graphics at pure 1080p 60 fps. It was clearly meant for the PlayStation 4; not the PlayStation 3.
