I would be interested to see Data / Signal / Image processing dual channel bench test vs quad channel bench test?
It is simple, think of taking an array, very large array (25,000 x 25,000) and just add it a constant to each element.
Think of having 2 of those and just multiplying element by element.
Apply 2D convolution on it with very small kernel (5 x 5).
Let's do the math for the first one.
The CPU has 4 cores each has 2 AVX units (If I remember correctly).
Assuming the array is float, the AVX can handle 8 elements per cycle.
At 3 [GHz] it means:
8 [Element] * 4 [Bytes / (Element * AVX Unit)] * 2 [AVX Unit / Core] * 4 [Core] * 3 [GHz] = 256 [Bytes] * 3 [GHz] = 768 [GBytes].
Namely for highly dense AVX operation (As Signal / Data processing is) we'd need 768 [GBytes] of bandiwdth.
Of course it is unrealistic, and we have memory hierarchy but as you can imagine, with large arrays and the small caches it means that at some point the CPU will be waiting for data from memory.
Hence any increase of that will benefit the overall performance.
By the way, for instant, Gaussian Blur in Photoshop on 48 [MP] image is totally Memory Bounded.