FPS Drops

I have a problem that appeared a few days ago after I've switched from Win7Pro to Win10Pro.

When I play and theres a lot on screen (enemies, effect, espacially Perandus mobs) my FPS drops to 10 and often even 3-4. Sometimes the whole screen freezes for a second or two with some strange looking effects for the skills.
I thought may be because of my graphics heavy Firestorm build, but even in Standard without Perandus mobs on my IceCrash Duelist my FPS drops significantly.

I also switched from HDD to SSD but that only improves loading times. I even went back to HDD with no effectts on FPS drops.
I tried all different graphics settings, also Lockstep and Predictive mode. With no notable change. High or low graphic settings also make no difference.

I havent monitored the load on my CPU and GPU all the time but when I did both weren't on full load.

Then I switched drivers back to the old Catalyst 15.1.1 beta, and thought it was slightly better but still pretty much unplayable with Perandus mobs. Then tried AMD Crimson Driver 15.12 with no success.

I know I haven't got the best rig but FPS was a lot better even with heavy effets and Perandus mobs on Win7.

My rig:
Phenom II 1100BE
ASRock AOD790GX/128
ASUS Radeon R9 280
8GB G.Skill 1066 DDR2
Crucial BX 480GB SSD


I think it has to do with Win7 and Win10 but dont know how to solve it. Any help would be greatly appreciated. Dont want to switch back to Win7.


Edit: I also tried the different window and full screen modes with no difference.
To narrow down reasons for fps drops I started my old windows 7 installation which still worked and voila no fps drops anymore, at least not as bad as in win10.
Next i try to disable the win10 desktop effects to see if this has something to do with it. Of course it could also be the amd drivers.
Any other ideas?

Edit 2: Disabling Desktop FX had no impact. I also did a hardware "upgrade" (MB MSI 970A-G43 Plus and 8GB DDR3 RAM Crucial Ballistix in Dual-Channel mode. Again no improvements. Game gets still unplayable wit 1-3 FPS and seconds-long freezes.

Also I know now why nobody answered. It is a well known Problem (See this thread https://www.pathofexile.com/forum/view-thread/1317177).
Nevertheless will I use this thread to document what I do to improve. And because I can clearly say what causes my FPS to be much worse: The switch to Windows 10. I have the FPS drops on Windows 7 too but the game never gets unplayable like in Win10. Maybe this helps someone or GGG to work/solve this issue.