FTB Unstable 1.12 <5 fps, any ideas?

What I thought of:

• It's not videocard as GPU Load <50% (Radeon RX 480).
• It's not CPU as CPU Load < 20% (i7 3770k).
• It's not RAM as Minecraft only takes around ~2GB of dedicated 4GB of ram (-Xms4G -Xmx4G).
• It's not multiplayer issue as it occurs in single player too.
• I've tried Forge from pack (2413) and a newer Forge (2420).
• Java is 1.8u111, 64 bit. Windows is 10. Catalyst is 17.6.2.
• OptiFine added 2 FPS, so it's <7 FPS now.

Screenshot – https://i.imgur.com/WFZiUEA.png

Friend of mine has same problem with Catalyst 14.12.

Any ideas?