If your getting decent FPS in fallout 4 at medium settings an upgrade really isn't nessicary unless it is just a for the hell of it thing, witch I understand. If your looking to get better fps a new GPU would come first assuming your power supply could power it and it fit in your case. An upgrade to an i7 would be nice, preferrably 4770k or 4790k. Hard drive and SSD are fine. You could grab some extra ram also. IMO I would stick with what you have for awhile and just sacrafice lowered settings untill you have enough money for a full upgrade to something that can run current games at max.