I used the iMac definition trying to get HTML5 work with Safari. The boot time is usually quite fast (not as fast as windows though) but sometimes takes a bit longer and I don't know why it does that.
Thanks. I just finished installing 10.11.4 from scratch and all is fine.
My observations:
1. MacPro3,1 is no longer OK for Skylake, as something changed in 10.11.4 that makes using the MacPro3,1 buggy (slow boot times, buggy CPU power management, etc)
2. Install using iMac14,2
3. Once installed, switch to iMac17,1 (native Skylake support) and don't forget to apply the graphics patch needed for this definition
The resulting system with the iMac 17,1 definition:
- iMessage works just fine
- CPU power management is incredible, the CPU actually runs cooler than in Windows 10...
- Turbo works perfectly - though remember to use an SSDT file for your specific CPU
I think I will write a guide since I have everything working flawlessly