Installation
The PlayStation 3 version has a mandatory 3.4 GB hard drive installation that will be the longest 7 minutes and 20 seconds of your life if your chomping at the bit to play. It's initially an annoyance, but PS3 owners will welcome it. There is no option to install the game to an Xbox 360 hard drive.
Frame Rate
The Grand Theft Auto series has never been synonymous with a rock solid frame rate, something it generally seems to get a pass for. While GTA IV is smoother in general than it's predecessors, it can expectedly suffer during chaos. The Xbox 360 version seemed capable of achieving a smoother frame rate, peaking higher in certain circumstances, such as in confined spaces or during light traffic, but both versions seemed to regularly run at a similar clip.
Pop-In & Loading
With a huge, seamless streaming world, data must be constantly read from the disc. The PS3 version, with its required HDD install, loads missions a couple seconds faster and decreases pop-in. The Xbox 360 version can suffer from some very noticeable texture loading, as things like trees, vehicles and building signs will regularly pop-in as one tools about town. It can be distracting, especially during high speed chases, and the PS3 version isn't entirely immune from it, but it's not a game killing problem.
Graphics
The two versions are so close to identical, visually, that putting together a comparison was a challenge. Initially, it appeared that the PS3 suffered from more noticeable aliasing than its 360 counterpart, but after eyeballing the final retail copy, they appear to be on par. I noticed that the paint filter applied to cover some of the game's imperfections appeared a tiny bit muddier on the PS3 version, with night time scenes seeing more streakiness. Some of these minor complaints may be the result of our particular television settings and require the finest of fine tooth combs to assess.