Earlier quoted context omitted.
For the C++ codebase I work with my 6700 compiles 4.5 MLOC of code in a little less than half the time my 2nd gen i7 does. Hardly scientific, but the 6th i7s are really fast.
This is probably due to the improved storage iops of a PCIe flash drive more than the CPU.
That and all 8 cores (I am counting the HT threads as cores) in the system monitor are fully saturated on both machines until the the linking stage of the build. I have a great deal of confidence the newer CPUs are significantly for at least building C++ code when disk bandwidth is not an issue.