The Intel HD 4000 graphics core beats the HD 3000 hands down, with performance leads as high as 122% in a particular test. The chip produces more than playable frame-rates with Left4Dead 2 and Street Fighter IV, both well above 50 FPS, even DiRT 3 and Far Cry 2 run strictly OK, over 30 FPS.
L4D2 isn't that demanding as its based on the source engine. You can probably get that running at 1080 with some details on. But Dirt 3 and FC2 could only muster 30FPS. At 720. No way those are going to be playable at 1080 with much of anything turned on. IGPs just aren't good enough to handle current games at 1080. They weren't designed to. In that article I linked they compare it to the GT240. Which is a very low end card. But the IGP in the 3570K is even slower then that. It will browse online and handle 720 ok. But it's not for 1080 gaming.