Poor FCLK voltage scaling on 4650G, bad mobo?

[askopte]

Originally my 4650g in my 2nd rig was set to 1.1V SOC, 1.4V memory and stable at 2066MHz FCLK and DDR4-4133 C18-22-22-42. (unstable beyond that at 1.1V SOC)

Last night i tried to improve upon this and set the SOC voltage to 1.15V and FCLK is stable at 2133MHz. But when i tried 1.2V SOC today it doesn't seem to scale beyond that. 2166mhz is unstable and 2200mhz won't even boot. Increasing DRAM voltage doesn't work, and loosing timing also doesn't work so i assume that's a FCLK bottleneck. 

In other words, 0.05V increase on SOC voltage lead to no improvement on FCLK at all. Do i hit a limitation on the motherboard or there are other problems?

 

Spec of my 2nd rig:

CPU: 4650G, SOC 1.15V

Mobo: Gigabyte B450i Aorus Pro Wifi 

RAM: Crucial Ballistix 16GB, memory IC is Micron rev.E and part number is C9BLM (in thaiphoon). Stock XMP at 3600C16 and now stable at 4266C18-22-22-42 1.4V. subtimings are as loose as possible