From the information I can gather, it seems like you have a Intel i7 processor. These are some of the latest chips from Intel and it should be able to perform fairly well.
Have you tried running speedfan or another temperature program yet?
Does your heat sink for the processor need cleaning? (I use compressed air & Q-Tips/ alcohol to clean)
Maybe you should buy a aftermarket heat sink.
The graphics cards you link would be a nice upgrade for sure. I think which one you buy is just a preference. I personally like the XFX brand. I have had 3 of there gpu cards so far.
If I was in the market for a new hard drive I would consider an SSD for the operating system. Then use the old hard drive you have to load everything on.
http://www.newegg.com/Product/Product.aspx?Item=N82E16820148441 Or something like this one if you don't want to go the SSD route. I like the hard drives with a 5 year warranty.
http://www.newegg.com/Product/Product.aspx?Item=N82E16822136533 this one is smaller but cheaper
http://www.newegg.com/Product/Product.aspx?Item=N82E16822136794