i have done an initial outlay cost of the 680 and it will set me back £510 aproximately for the GPU and waterblock.

That is about as far as i would go for a high end GPU that needs to be kept and used for 2 years minimum. i always tend to try and skip a gen or two in GPU land and not one of those folks who upgrade a GPU every year/gen So really your looking at the cost of this GPU being 250 per year for 2 years

Now if u was to but a 6xx nvidia or 7xxx ATI thats 250, it wont cut it and u will most definetly have to upgrade that gpu again next year so in theory you end up paying £500 in total in a two year stint.