Re: cpu - dual or quad?
It depends what you use it for. From your list, games and video editing will benefit, as will, to a point, video capture, beacuse more load will be on another core, freeing up clock speed of the others. For the other applications, if you are using several of them you will again see performance increase, but it will be mainly down to the clock speed that you have it at, rather than the number of cores for your single threaded programs
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