From a technical standpoint, the HD4000 should be slower than the GT 650M. If you observe results that show otherwise, I would think it's something to do with how the GT 650M is being utilized. You should have at least one program that can monitor GPU activity, at least for the GT 650M. If you notice that GPU activity is low on the 650M, there's your culprit (this was a problem with some desktop GPUs, not sure of it applies to laptops).
What are your graphics settings? Also, which games are you playing? Post screenshots of the General, Hacks, and Enhancments tabs. Try setting your IR to 3X. This should kill the HD4000's performance, but the 650M should be good; that might also force your computer to use more of the GPU's resources if it isn't already.
What are your graphics settings? Also, which games are you playing? Post screenshots of the General, Hacks, and Enhancments tabs. Try setting your IR to 3X. This should kill the HD4000's performance, but the 650M should be good; that might also force your computer to use more of the GPU's resources if it isn't already.