I wouldnt worry too much about the quad core recommendation... actually I dont think it will make a huge difference once you turn the graphics and AA up, it will be GPU limited even at 1680x1050.
Hyperhorn, although GTA IV does use quad core quite well, it would be more fair to compare a Core2Quad vs the E8600... i7 is MUCH faster than the penryn/core architecture and that i7 920 would eat even a quad of the old generation!
In GTA IV once you turn the Graphics up you become GPU limited... but yes quad in that game does help.
PCGH now lets see a benchmark review... the world is waiting and I have been on a few ARMA2 forums, anticipation is huge about how it will run on peoples systems... if you could get a benchmark out first it would be great
I dont really believe in published min/recommended specs... their always way under what is really required (they want to sell the game)