Current guess-timates indicates that the Intel HD 4600 (GT2) is estimated to be about 20% more powerful than a similarly clocked Intel HD 4000. Note that while all mobile Ivy Bridge CPUs have the Intel HD 4000 graphic core, they do not all run at the same clockspeed. Ivy Bridge CPUs with the "Y" desgination have the lowest performance to decrease power consumption. "U" model ivy Bridge CPUs are used in ultrabooks and are the 2nd slowest Intel HD 4000 clockspeeds. Dual core i3/i5/i7 "M" CPUs will more or less have "standard" performance. The quad core i7 "QM" CPUs will have Intel HD 4000 with the highest clockspeed.
All together, there are about 7 or 8 different clockspeed variations of the Intel HD 4000 in mobile Ivy Bridge CPUs. The...