If you can afford it, the WD Black SN750 is excellent (I have 2 of them). It's only PCI-E 3, but it's very fast and at the moment OCUK have it for £120. Alternatively the WD Blue SN550 is also good. Not the fastest PCI-E drive but fast enough that for most purposes you won't notice any difference - and it's sub £100.
My friend has just ordered one of those Sabrent drives - he may already have it, so I'll see what he thinks of it.