And Finally...
After almost two thousands words of technical discussion, the bottom line is that it's clear that Rockstar had some issues matching the basic performance of the Xbox 360 game on the PS3 hardware. Lower resolution, zero anti-aliasing support and a more variable frame-rate are the bottom line.
On the one hand, it's a touch disappointing that Rockstar's USD 100 million budget couldn't extend to optimising the experience to match Xbox 360, especially when you look at a game like Burnout Paradise that doesn't require a mandatory installation, has a basically rock solid frame-rate, and is technically identical cross-platform.
That said, it's patently clear that Rockstar hasn't handed in a lazy conversion here. Creative decisions have been made to compensate for the technical limitations, and by and large they really work, to the point where you sometimes wonder why they couldn't have been applied to the Xbox 360 version too. PS3 GTA IV looks absolutely fantastic, and even factoring in zero anti-aliasing support and a lower resolution, in many scenarios it looks as good as the 360 version, if not better.
I've not addressed the freezing issue being reported on the game, of course. I'll have to leave that to the people affected as - try as I might to coax the code to fall over and die horribly - GTA IV behaved impeccably for me on both systems. But the chances are that by the time you read, a PS3 patch will be out and about that should sort out those who've been affected. A 360 update after that, please, complete with a tweakable option to use the PS3 post-processing modes. Now that would be interesting.