Depends specifically on the CPU model some CPU are just a little higher clocked. For example,
In the i5-3230m the Intel HD 4000 base clock is 650MHz and max is 1.1GHz.
http://ark.intel.com/products/72056
i5-3380m : Intel HD 4000 = 650MHz / 1.25GHz
http://ark.intel.com/products/71256/Intel-Core-i5-3380M...
i7-3520m : Intel HD 4000 = 650MHz / 1.25GHz
http://ark.intel.com/products/64893/Intel-Core-i7-3520M...
i7-3840QM : Intel HD 4000 = 650MHz / 1.3GHz
http://ark.intel.com/products/70846/Intel-Core-i7-3840Q...
The i5-3230m is a pretty common mobile Ivy Bridge CPU where the Intel HD 4000 runs at max 1.1GHz. It's not the slowest speed, but certainly not the fastest. Only the more expensive quad core CPUs has the Intel HD 4000 running at it's top speed of 1.3GHz. However, those CPUs are pretty expensive.
You may want to consider a laptop with Intel's Haswell CPU which has the Intel HD 4200, HD 4400 and HD 4600 integrated graphics core. The HD 4600 is the most powerful of the three which I believe is about 25% more powerful on average than the HD 4000. There is also the Intel HD 5000 series with "Iris" being the most powerful graphics core which is the Intel HD 5200 + eDRAM and it is roughly equal to a nVidia GT 640m GPU, but they will be on the higher end laptops.
So far, the only laptops with Haswell CPU only have the the quad core i7-4xxxMQ series which has the Intel HD 4600. Since Haswell CPUs has only been recently announced, less expensive dual core i5 mobile CPUs should be coming out shortly.