I'd change the motherboard to an MSI Z77a-G45 as Gigabyte Z77 boards aren't the best.
And I'd also change the SSD to a Crucial M4 or Samsung 830.
I'd also think about a better case. Nothing wrong with the Shinobi, but for an extra £10-20 I think you could do quite a lot better with something like a CM690, or one of the Fractal cases.
James has got it spot on so all I can do really is echo what he has already said For Z77 MSI over Gigabyte, I notice that Gigabyte board is about the price of a GD55 so I would recommend that.
I have a 690 B&W edition myself and I think it is a pretty great case for the price tbh
What they mean is that the Gigabyte Z77 boards are not bad, but not as good as MSI Z77 boards. If you are on a tight budget then go with the Gigabyte UD3H, it's a decent board.
Plextor ssds are very good, especially the one you originally planned on getting. Msi have gotten the best mobos for z77.. Just dont expect to get your rebate back