I do not have that specific processor, but given the other specs you listed, I'm almost certain that you are being bottle-necked by your RAM rather than CPU.
I'm running the game on a much older, slower processor, an i5-2320 @ 3.0Ghz, with an 8GB RX480, which is roughly equivalent to your GPU, but with 32GB RAM. In 1080p with all settings maxed, my total CPU utilization rarely goes over 50%, despite running a SQL Server instance in the background, Chrome with 60+ open tabs and hosting a media server.
On the other hand, in the second act the game EXE's RAM usage frequently jumps well into 4GB+ territory, especially in crowded areas like Driftwood. With your system running on 4GB total, that would definitely be problematic.
