A new processor would be a nice improvement. The extra HDD would also be good, don't waste any money buying an SSD for recording, unless you put your OS on there. Also, have you tried open broadcaster software? It is quite good for recording and gives you a large number of options, including recording multiple sources (eg, webcam and game at the same time).
What resolution are you recording at? Your current setup will work better if you record at 30FPS and scale to 720p. (unless you are already doing that)