I have also noticed some performance issues with the chip.
When you say you disabled C-States are you talking about bios settings or have you changed the cpuspeed governor to performance?
I have been experiencing an extremely low throughput in a pfsense vm hosted on my centos 6.9
Changing governor to performance has improved things considerabl, even though I am still having trouble hitting my max ISP speed which is supposed to be 40mbit.
I am getting up to 30 with average around 22mbit/s.
The other problem is that I can't really change any bios settings without wiping bios because the motherboard fails to recognize my sata ssd unless it is in csm mode, but in csm mode it is impossible to enter bios (at least that was the case with 1.2).
I plan to try and install bios 1.3 and see how things are, but probably won't do it in the coming days.
Issues related to hardware problems