Hello, pretty much same issue here.
My specs:
cpu: amd fx 8320e
gpu: radeon r9 380
ram: 16GB total
disabling vsync increased fps from 20 to 40+-, installing vannila fix increased the fps from 40-60 to 100. I also have optifine, and I changed the priority of javaw.exe in task manager to high (not real time), but that didn't make any difference for me. I was playing on an outdated version of E2:e yesterday and didn't have any fps issues so it's really wierd to me. also i do not have any integrated gpu.
I though my pc could run E2:E on average 90fps, without any extra software, so i dont really count this as a fix, but rather as a workaround. But then again, amd graphics cards do have some wierd issues like even enabled mipmaping causing massive fps drops.