It would help if we knew what cooler you had for your CPU as you could definitely gain performance from overclocking.

i put that on the post,i have a noctua nh-d15s cpu cooler.here is my speccy stats if that helps
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With that cooler, definitely look into overclocking before you go ahead and buy a i7 and just so you know
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so before i go ahead and pay 300 pound you recommend overclocking,will i get any difference from getting an i7 over overclocking,sorry for the silly questions

Well you wont get hyper threading with your i5 like you would with a i7 but you should see a improvement with overclocking your i5.

is hyper threading going to make a massive difference? thanks for the advice,i will look into how to overclock as not sure how

No, Hyper-Threading won't make a massive difference. But with your cooler i would look into overclocking your i5. But if you dont want to do that. If your going to buy a i7, Make sure the socket is right! So since you have the 4790k its a 1150 socket so look for a i7 that has a 1150 socket.

Overclocking your 4690k will definitely give you better performance. You should go ahead and OC your i5(as long as you're comfortable with it) and keep using it. If you feel it's not performing as well as you'd like, then you can look at an i7 maybe. Your best bet would be a 4790k. Though, if you really have no interest in overclocking, you could maybe pick up a Xeon E3-1231 V3. Then sell your 4690k to make most of the money back. The E3-1231 V3 is basically an i7-4790 with no iGPU, so you need a dedicated GPU(which you have anyway, the GTX 970) and you it's a locked chip so you can't OC it. The E3-1231 V3 will perform about the same as a stock clock 4690k in single threaded applications/games, but will out-perform the 4690k in multi-threaded situations.