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Does it matter whether the chip is Malay or Costa Rica for better overclock?
is it worth the upgrade to 3770K for £50 more if I sell my current CPU?
Entirely dependent on your use, it is worth it in general, but unless you are doing CPU intensive tasks like video editing I wouldn't bother.
For gaming, yes you would see a difference, but you would probably benefit more by investing the money in a GPU upgrade.
I have Sapphire R9 290X Tri-X graphics card and the computer is used for university such as word processing, a little bit of VMWare, Photoshop and video editing as well as gaming in my free time however I don't intend to upgrade my system except from the graphics card in 5-10 years time.yes if you will use the extra threads. if for just games no
if you sold your CPU you could get a NEW i5 6400 for about £50 extra. now that would be a massive upgrade
What GPU do you have