Not really sure what part you think would bottleneck. CPU and GPU are really doing different duties when it comes to rendering and streaming. Rendering is really going to be primarily up to the GPU with the CPU feeding it information. Streaming is all about data transfer managed by the CPU. An i7 isn't going to be any faster per core then an i3, it just has double the resources. Basically what you are accomplishing is separating your streaming from the needs of the game engine. This will improve overall performance, but not change any bottlenecking between your GPU and CPU.
Short version. Your GTX960 isn't bottlenecked now, and an i7 won't be bottlenecked by a 'weak' GPU. CPU will just have more cycles to do what it needs and the GPU will show more or less the same performance. (Maximum frame rates will by the same, minimum should improve)