|Consider how much your complete upgrade will cost you over the coming months and compare that cost to the price of purchasing or building a new system. You probably would find that there is not that much difference really. Consider starting over if the cost is close.|
You can upgrade the power supply without worry. You could use a 1000Watt unit but if your combined draw is only 200Watts, that is all that will flow into your system. Practically, the 1000w watt unit would not be cost effective for you, but a 500Watt or 600Watt unit might make sense. It is important to purchase one with a single 12 volt rail and 80% efficiency rating, and to shop for your graphics card first to see the requirements as far as Wattage AND Amperage on the 12 volt rail.
Remember that if you upgrade your PS, Your MB, your GPU, you will end up adding to or replacing your RAM, and you still only have a Pentium E6600. Would you then think about upgrading that??? Probably! You really should consider a fresh build, something brand new, modern, and fast, that you would be happy with for a number of years rather than dumping more money into each month or so without ever really achieving that really fast system you are craving.
Look at the 2nd generation i-3 or better and a reasonable socket 1155 board (Gigabyte has some with nice features at a decent price range), DDR3 memory, etc..
You have to be a little bit crazy to keep you from going insane.