3) RAM: We'll leave the same for now, as Cas9 isn't a show stopper.
4) PSU: This is one of the areas you don't want to skimp on quality for price. I would go with this one for a single card setup... Corsair CMPSU-550VX
5) CPU & GPU: They are actually some what balanced to a point. If budget permits, I highly recommend a higher level GPU to at least a GTS 450 or ATI 5770. For your CPU, I would recommend the Phenom II X4 955 though for the better CPU.