The Corsair VX is a terrible buy for 67 pounds, it is a good power supply but it is at the wrong price. For only 3 pounds more you can get this: XFX 650W XXX Edition 80Plus Bronze, Modular
£70. You can even get this, which is more powerful, more efficient, modular and cheaper: Be Quiet Special White Edition 80Plus Bronze, Modular
The problem with the 400CX is that it only has one PCI-E power connector, which is an indicator that it is a tad light on power for a video card that needs two.
The only other thing I would change, if it was my build, would be the case. But only because I don't like the look of that Casecom and I'd prefer to get something more expensive.