If a bottleneck is possible as previously tested on a 7850 when using an i3 3220 with Hyper Threading giving 4 threads then you can be sure it will be even more noticeable on an older gen i3 with only two cores. 40% gpu usage missing from skyrim and 30% missing from Sleeping Dogs which is a gpu dependant game. You can probably expect even lower usage with an older gen cpu with less cores.
Let's say the OP takes your advice and buys a 7790. Nothing wrong with the GPU and a card suited to the very casual gamer, it will probably still bottleneck but let's not worry about that for now.
Now in let's say, 9 months time, the OP is a fan of Crysis 3, Battlefield 4, Tomb Raider, blah blah blah, the 7790 isn't really the card if the OP decides he 'very much enjoys gaming on his PC' and likes the smoothness/gfx detail that the PC offers. He has spent his money on a 7790 and will need to upgrade that, as well as his CPU. At least if he buys a 7850 or a 660, he only has to upgrade the CPU.
You see my point? It is all about having further options in the future and possibly saving a few quid.
When we take this bench result, you can clearly see it isn't up to max details and playable with either a 7790 or a 650TI in my opinion but owners of a 7850 and a 660 will tell you it is playable on their system. I am not saying the OP wants max details but if in the future he decides he does, he already has the GPU to give him that option and just needs a CPU to go with it. With your way of thinking, he would have to get a new GPU as well as a new CPU and for the fact of £15-£30 on the original purchase, I just don't think it is worth that saving.
And you had the cheek to ask what planet I live on....
Ohhh and the OP has already said he isn't adverse to upgrading his CPU in the future if needed or are you just wanting to make me look wrong and in doing so, cost the OP more in the long run?