Upgrading to Mavericks took around 40 minutes on my system and the Windows 8.1 upgrade took 1.5 hours. I don't see your problem.
Install speed has little to do with your CPU, but more with HDD and USB read/write speed.
Since a short while I haven't been able to boot my hack with UseKernelCache=Yes. I normally use it because it makes Mac boot faster. I've booted in verbose mode with UseKernelCache=Yes and this is what I get:
Apparently, IOACPIFamily.kext is the problem, but I don't really know how to fix...