Short as possible w/double run - even if you have to buy cheaper cable to do it. I've heard that from R. Vandersteen, and his advice always seems to match experience.
I've read in a few places that buying two runs of cable brand X will outperform the biwire version of cable brand X. This would make sense from an interference perspective. One of my friends who was a solid state physicist mentioned that twirling a biwire set of cables would help to cancel out frequency interaction, but separating them by 6" or so would be the best. I did the twirl, but do not hear a difference. I do hear a difference if I raise the cables off the floor.
