What exactly have you done in terms of installation? I have the Gtx 650 in my build (evga 2GB SC) and the fan is noisy (sounds like its running at 100%) and I can't play video without my system crashing. What system definition did you use? Could this affect my performance? I'm on 10.8.0.
Installation for me was rather simple. I had the system already running using the onboard HD400 video with 2 displays, 1 on DVI and 1 on HDMI using MacMini 5,1 system. This was done with GE=no, and defining the device properties in the org.chameleon.Boot.plist per the build write up for my GA-Z77-UP5TH.
For installation, I shutdown my system. Installed the physical GTX650 GPU into my X16 slot, booted into the BIOS and set to Init the PEG display first but also for embedded HD4000 to be enabled. I then saved the BIOS settings and shutdown.
I disconnected 1 monitor and connected it to the GTX650 and booted, once booted OSX detected the 2nd display correctly. I then unplugged the "first" display and moved it over to the GTX650 and it was also detected correctly. I set my display arrangement to my preferences and have been running since. I have 1 Dell U2410 on DVI and one on HDMI, would have both on DVI except I only have 1 DVI cable and it works...so why spend the $ on a cable?
I have not done any of the power management edits as it has been fine and why fix what isn't broken? I did delete the FakeSMC.kext/Contents/PlugIns/OemSMBIOS.kex file after upgrading to 10.8.2, but that has been it.
I've been rather fortunate, as my Hackintosh (my first) was super simple to build and has been in use as my every day work computer and has been rock solid. I am running 10.8.2, I have custom SSDT.aml allowing me to get 7 speed steps up to 4.4GHz, the system runs <40 degrees most of the time and typically in the mod 30 degree range. This is a GA-Z77-UP5TH, i7-3770K, 32GB Corsair Vengeance, Corsair H80 cooler, onboard NIC, etc. Geekbench of 15035:
http://browser.primatelabs.com/geekbench2/1060308