Total newbie here. It's not really about overclock, but I couldn't see a better category.
I've been told before that (other parts being more or less the same) 2 cores @2GHz is not going to be as fast as a single core @4GHz, because you don't get the sum total.
What would be a reasonable guesstimate? 60% 75% 85% of the output of the single core running at 4GHz?
If we can label this "efficiency", what would happen as the core number increased? Would you expect (other components being about the same) the efficiency to be about the same, to decrease or increase?
Is there a rough way to estimate "efficiency" based on core number as a guesstimate before you get to see the benchmarks?
It doesn't work that way due to threading. Some tasks are single threaded, and at this point in time will always be that way. In this case it doesn't matter how many cores you have, it will always run on only one core. ("efficiency will go down then as the cores go up.) Other tasks will respond quite well as the cores go up. Video transcoding for example runs better on the 6 core AMD 1055T rather then the 4 core i5 750, even the 750 is stronger clock for clock. In this case your better off with the dual then the single.
As we develop better programing languages that do a better job of threading, the dual core will be better/faster then the single core CPUs. We aren't there yet, and no telling when we will be.