I know I am deviating a bit from the original HD 7670M Vs GT 630M discussion, but it does not hurt to know where integrated graphics is heading in future. In 2013 Intel will release three variants of Haswell graphics, GT1, GT2, and GT3. There is not much to write about GT1 and GT2 which will of course be better than the HD Grahics 2500 and HD Graphics 4000 that we have in Ivy Bridge today, but the the top end part, GT3, has 40 of the enhanced Ivy shaders ( There are other reports that say there are only 20). By contrast the HD Graphics 4000 has only 4000 today. Even if GT3 does not increase GPU clocks at all, has zero performance enhancements, nor anything else, it will be 2.5x faster than the Ivy Bridge. Ivy Bridge is 2x faster than the Sandy Bridge. So, Haswell is 5x faster than the Sandy Bridge.
Just multiply that with the integrated memory, performance improvement per core and the Haswell is a graphics monster.