Who's to say NG2 will be perfect? DMC4 is a rock solid 60 fps with no tearing 98% of the time. Slowdown is extremely rare (though I've only played up through chapter 9, but that is after the forest). There was one area in the forest where I noticed it dip a tad, but it wasn't really bad.
It's not about "X effect" either. I felt that the advanced lighting in DMC4 gave the scenery some truly remarkable depth. The environments in NG2 are completely flat and devoid of lighting.
Which version of DMC4 have you played? I've yet to encounter ANY tearing. Very minor slowdown, yes, but absolutely no tearing. V-sync is enabled at all times.
Ah, you're on the 360 version. That explains the tearing and severe slowdown. I just played through the forest stage last night on PS3 and thought it looked awesome (though the shadows are jaggy, but that's generally not the case in other areas). There was only one area where I encountered slowdown and it was very minor. No tearing. Outside of that one area in the jungle, the game has been a solid 60 fps. Even the cutscenes run at 60 fps a good portion of the time (though they do drop in framerate at times).