Mutation forces organisms to explore evolutive paths quite astray and I'd expect it happens quite often that a 2 gene mutation propagates into the "global pool" for being very advantageous. Of course, specific or optimal 2 gene mutations are wildly unlikely to be found.

What I mean is, a more adequate picture of the process is not a simple "path" analogy. It's more like you have a high dimensional optimization space and a wildly varying survival function, and the organisms are bouncing around this space in a random motion. This allows them to occasionally cross valleys and take very distinct paths to each far away maxima, specially if there are a few minor maxima along the way.

My point being organisms have a given capability to bounce around: they don't have to take a monotonically improving path, although this capability is limited because otherwise (if the mutation rate is too fast) the results are too chaotic.

They're somewhere in the middle of monotonically improving, guaranteed optimization (low mutation; gets stuck at local maxima) and completely random (high mutation; does not retain advantages well and leads to many deleterious results).