I doesn't seem to be "building the kernel"...
Did you get it to work with the older kernel?
Is there any particular reason that the CUDA miner would only perform at maximum khash/s if its CLI status window were the foreground window?
No. The hash rate is constant here whether the window is in the foreground or background. You can try different graphics drivers (newer AND older) to see if that helps. It could also be something with Windows 7 interfering with the priority of background apps.