Does the GPU run at the base clock or the turbo boost clock most of the time in games? I'm curious because of the lower base clock of GT3 vs GT2 in Haswell (200 and 400), but the turbo clock is about the same. The GT3 has double the execution resources, but if it runs at half the clock speed most of the time the performance gains would be lower. If it's always hitting turbo that's a different case, but then why call it turbo?
And is the double performance claim for the GT3 with or without eDRAM? It seems getting up to double the performance you would start to be memory bandwidth limited like AMDs APU GPUs are, so it might be with the eDRAM?
I would say that similar to the clockspeed of the CPU core, the GT2 and GT3 clockspeed will be based on whether the iGPU is being stressed or not. If you are not doing anything too demanding like writing a document, then the iGPU will be running at it's lowest clockspeed. When watching a video the iGPU must decode the video so it will be running above the minimum clockspeeds, but less than it's maximum clockspeed. Playing graphically intensive games should force the iGPU to run at it's highest speed (depending on the temp). However, if the temperature of the CPU increases beyond a certain point, both CPU and iGPU clockspeed will be reduced to prevent damage.
As for the actual performance increase of the Intel HD 5000 vs HD 4000... thus far it is unknown.