KatakunaZu

@robi62
It happens on mine too, doesn't affect performance in any way at all. If you enable SpeedStep, then you will get the weird, out of sync video and audio stutter. I think this might be a PowerManagement issue or something, I'm not sure, might need to look into it more.
For now, it just works 

I just used the the kexts provided by OP. I believe the Quadro NVS 160M is using native kexts. Are you only using DisplayPort or using a DisplayPort(DP) to High Definition Media Interface (HDMI) adapter? I'm using an adapter, maybe try to source one from somewhere, if your monitor supports HDMI.

@bootxy Do you have hwmontor installed to see what temps cpu get too

 

When problems happens are the fans on????

 

What smbios are u using????

 

for kextstat you just type kextstat in terminal it gives you a list of loaded kexts then save it with textedit

@robi62 About your issue with the CPU, the P8600 runs at 2.4 GHZ. Some CPUs are not exact, as mine runs at 2394 MhZ. Is it a big issue like it running at 1.6 GhZ? 

@bootxy When you turn the system on, hold down fn+LShift and type 15324. The press fn+r. This takes you to a hardware monitoring bios setting display, where we can see your temps, fan speed, CPU throttle, power throttle. All these could contribute to the issue of the random shut downs.

Report back, and I'll check your issue.

Sorry for not being able to help people, I am hardly on anymore, except for a major OS release or something. Feel free to PM me and I can sorta help xD 

DisplayPort works perfectly fine. Can't seem to get it running on the docking station though. Also if you use a power adapter that throttles your CPU, your computer will run kinda like in slow motion. Time will be behind by like minutes or even hours. SpeedStep being enabled does the same thing.
For Wireless, I have a secondary Apple Branded Broadcom 43xx card in mine, and it works perfectly. I had accidentally updated to OS X 10.10.4, only thing I can see being replaced is the audio kext. 
Happy hacking! 
Also note: If you use DVI at resolutions above 1600 x xxxx, you're gonna get white noise. Sleep the computer for about 2 seconds then press the button on again. The computer fans shouldn't stop whilst doing this.

EDIT: I had a look at my BIOS settings. All the things that the second guide told us to disable was enabled, except for VT for Direct IO. It may just be my machine, but try it and see if it works for you.