Long story short, my XFX 7950 had a fan failure, sent it back and got my money refunded. Now back in the market for another GPU.
The XFX 7950 cost £170, there is now a 280 equivalent available however it is built by XFX and I don't want to use that brand again based on my experience.So let's say around the £170 mark is my budget.
I really think the choice should be based on what games you're going to play. The 270x is going to be able to play most games on high/ultra at or close to 60fps. The 280x is just going to do a bit better in some games. Look at some benchmarks for the cards and have a look.
Keep in mind that the 280x are essentially on a waiting list globally as far as I've experience, and the prices are subject to go up and you will be asked to pay more if the price does increase. the 270x don't seem to be selling quite as ridiculously and I wouldn't be surprised if you were to get a 270x from MSI or ASUS that you could OC it within reasonable temps to be close to a 280x
280x are in stock in the UK, there is even a 280x for £199, but the brand is VTX3D (Similar to PowerColour) I rather buy a brand like Asus though after my XFX fan failure.
Doing some research online, the 4gb version of 270x only makes sense if you crossfire, but I only plan to run a single GPU, so I've decided to invest more money in 280x, plus it will be better in the long run.
Just ordered a MSI Radeon R9 280X Gaming Edition OC 3072MB GDDR5 for £199.99 to be delivered tomorrow, stay tuned for a rebuild as I've ordered a few other parts too.