my budget is £300, i use my pc mainly for gaming. i was thinking of upgrading to the new zen+ 2700x. not sure if i need to get that one, or should i go with the 2600x. and get more ram to get up to 16gb ?
I personally would look at buying a larger SSD and faster RAM (Ryzen loves fast RAM).
Even if the 120GB SSD offers enough space for you, that small of a drive generally offers inferior performance compared to their larger siblings. Lastly, DDR4 2133 is too slow for your CPU. I'd look at getting 16GB of DDR4 3000 or so.
You can always upgrade the CPU if it's your bottleneck, but if you are a gamer, it should be more than enough for you right now (especially with a GTX 1060 3GB GPU). Even if you upgraded to the faster CPU today, you still would be held back by the first two items I mentioned.