My Rig Struggling With Fall Out 4

So i recently purchased Fallout 4 looking forward to what seemed like a widely popular and exciting game. However i'm having major issues in terms of stuttering and jerkyness thats making the game unplayable for me.

I've tried different tweaks and settings (including changing to the lowest possible) and it still ruins it. It can be fine as long as nothings happening, but as soon as theres action like movement,shooting or im turning/strafing alot it becomes sticky and sometimes locks up for a minute or so. Below is my current setup, would you be able to recommend whats best to upgrade for me to overcome this?

OS:- Windows 7 64-Bit SP1
Processor:- Intel Core i5 750
GPU:- Sapphire Radeon HD 5850
Memory:- 4GB Kingston Dual-Channel DDR3
HD:- Western Digital WD6400AAKS

Thanks In Advance!!