So let my try to sum things up on the tech side. So many misinformed people here.
What we know:
Xbox 360 version runs at 720p with 2XAA according to "pro" pixel counter
MazingerDUDE.
What we suspect:
PS3 version is most likely sub hd. Has been speculated for months and was the same for GTAIV and Midnight club.
A resolution of 640p (which is not too far away from 720p) seems likely at the moment.
All we have right now are extremely bad off screen grabs from the PS3 version:
http://img571.imageshack.us/i/1050023.jpg/
http://img441.imageshack.us/i/1050026.jpg/
http://img683.imageshack.us/i/1050028.jpg/
http://img718.imageshack.us/i/1050029.jpg/
http://img59.imageshack.us/i/1050031u.jpg/
http://img514.imageshack.us/i/1050032.jpg/
http://img594.imageshack.us/i/1050030.jpg/
http://img210.imageshack.us/i/1050027.jpg/
MazingerDUDE had the following to say, based off the screenshots:
MazingerDUDE said:
I'd need direct grabs for some accurate analysis, but taking a possibility of overscan into account, the game probably runs at the same res as GTA4 (640P).
What we don't know:
Framerate on both versions
GTAIV initially ran about 10% better on Xbox 360. Episodes from Liberty City gave the PS3 engine a boost and improved the framerate up to par to the 360 version. Midnight Club sports a higher framerate on the PS3 (source: Digital Foundry)
Dithering on Xbox 360
GTAIV on Xbox 360 had heavy problems with dithered textures and shadows, decreasing the overall image quality greatly. This led to people preferring the PS3 version, even though it was inferior from a pure technical point of view. (720p 2XAA vs. 640p with blur filter)
(Digital Foundry, Quaz51 and IGN are prominent sources)
Update: Judging from the footage we've seen so far, the shadowing issue has been greatly improved, if not resolved.
The issue still seems to be visible on trees though. A direct feed comparison with the PS3 version is necessary.
PS3 Anti Aliasing
The original GTA IV PS3 had no AA, just a blur filter. Selective Quincunx AA has been added to the engine with the release of the DLC packs. Midnight Club implies Quincunx AA as well. An absence of any form of AA in RdR would be a disappointment.
Tearing
PS3 GTAIV is v-locked, 360 version had very slight tearing
Pop in
GTAIV streaming was pretty identical on both consoles.