Looks like your linkDistance is fixed at 20 (the default) and your linkStrength is dependent on connection strength? I think the canonical approach (as in, the one mbostock was thinking of, although I don't think it's made explicit anywhere, possibly deliberately) would be to have the linkStrength be fixed and the linkDistance be a function of the closeness of the connections (which I just referred to as "link strength" in my head, ugghh.) possibly with a correcting factor to accommodate for the size of the screen.
On a side note, this is one of the major troubles we've had with d3, in that a lot of it was obviously made with a particular use case in mind, but built to be much more flexible/powerful than necessary for that use case, which is the great strength of the library, but means that whilst the documentation of the api is extremely thorough, the documentation of the natural ways to use it tends to be done exclusively by example, which doesn't quite convey the understanding that lies behind it.
Ref: https://github.com/mbostock/d3/wiki/Force-Layout#linkDistanc...
