For me personally it is all about convenience and unobtrusiveness. I usually only carry one stand, an "onstage" weighted type, approximately 15" in height. Set up either actually on stage, or on a table at stage lip. I have an extension that can raise the stand another 7" or so. I have two mic bars, one about 12' and another probably 20". I will use the later for omnis. I don't think you need the type of spacing you are talking about for a simple two guitar setup. As to height, when a full band is playing I generally try to be at approximately the height of the snare. With the two guitar setup, your sources are probably less than a foot above the stage, so height is not quite as critical.