Which components in this system is worth upgrading ?

I now have a system consisting of following somewhat obsolate components MSI KA780G socket AM2+ motherboardAMD 64 X2 6000 3.1 GHz CPUKingston 4 Gb DDR2 PC6400 CL5 RAMASUS GTS250 1 GB VideocardSeagate 7200 rpm 500 Gb harddriveWin 7 x64 OEMI intend to place this with a new CPU in a Fractal design define R3 case My own conclusion about uppgrading this is 1) CPU AMD Phenom II X4 965 3,4GHz Black Edition (+Cooler Master Hyper 212+)This is what I consider the first and most important upgrade to do. I have great expectations for this CPU. Have seen customer reviews where it spontaneous is percieved as being somewhat faster than an i7 system and as good as a CPU released this year. If I get this CPU what is thenmy weakest part? Videocard? Should I overclock? 2) RAM I see that my mobo supports RAM up to 1066 MHz DDR2. Though ram is expensive. Is upgrading this meaningful? 3) My harddrive is getting filled up. How important is this component for FSX? I see several optionsa) Get one more cheap HD to get more placeB) Get another 500 Gb and set up a raid 0 array. That would in the first place give my 1 Tb in size and make an improvement just because of thatc) Get a SSD HD and have only FSX on it. But I have been adviced that the OS should always be on the fastest drive. So maybed) Get a velociraptor HD. Both OS and FSX (and also FS9 maybe) can be on the same and fastest HD 4) How limited am I by the videocard? What videocard should be significantly faster than what I got now? In the first place I will buy the case and the CPU + cpu cooler so future price changes can be taken into account. I'm using both FS9 and FSXand if my system could run the MS Flight fine. I use a lot of addon products for both FSX and FS9. Both scenery and planes.