For me, it´s working better with 600MHz base clock.
It´s more fluid when a very short peak of activity is needed (for example in fast forward or scene change in a high quality, high bitrate video) because of less lattency increasing clock.
And it uses the same power.
For me it´s very important the power consumption, but haswell do this very well and now consumption is more related to load than to clock speed.
My system (Intel 4570T with Intel HD4600 Windows7):
- Idle processor package (total) power= 5.8W
- Idle GT cores (HD4600) power= 0.03W
0.03W !!! is nothing and it won´t be less with a lower clock.
So I don´t see any drawback in the 600MHz clock.
Anyway, it would be cool to have an option to set the Intel HD4600 base clock, as you can change the processor base clock in BIOS and in Windows Power Plan / Minimum Processor State.