The Cooler Master GX series are crap, get that changed out. Everything else looks fine, 8gb would be the sweet spot for RAM but if you are low on cash I suggest you get one 4gb stick for now and add a second later on
The gtx 660 is as fast as the 270x. I would replace the PSU though. The 270x is a rebranded 7870 ghz edition which was launched to compete with the gtx 660. The performance benefit will be minimal. Your graphics card should be good for another year.
Yes as sreming34Egl said, the VS series from corsair is far superior to the gx series from cooler master. As i said before and sreaming34Egl reiterated, the performace difference will only be a small one.