Subspace Travel

Estimated travel times given in the Barnes-Gutierrez Hyperspace Engine entry are averages. The Quality Factors assume specifics about both the route and the vessel. For example the 1.00 Quality Factor for Major Routes assumes the route takes advantage of natural subspace topology and artificial stabilization using hyperspace drills. It also assumes an average arm stellar density. Near the edges subspace travel will be less easy and as much as a 10% penalty due to bad conditions are possible. Unforeseen subspace storms are also possible. However storms are more likely in areas of high stellar density than areas of low stellar densities. So in High density regions vessels might go faster, but they are more likely to meet unexpected gravity shear planes. Even in the best conditions a ship will be limited to no more than 10% over the subspace Quality Factor.
Further assumptions for travel along Major Routes are that the navigation beacon system is fully operational, and that the vessel has an operational VORN system. Similar assumptions hold for Blue Highways. On these routes the marking beacons are farther apart and the subspace topology itself not as structured. Department of Roads Storm Watch are less prevalent and the lack of an hyperspace cable system makes warnings a matter of minutes rather than hours or days.
Off the routes travel time is even more uncertain. If the destination world maintains a beacon, and if the gravitational topology is well known, a properly outfitted ship, that is one with a gravscanner and a quality Inertial Navigation System can usually maintain the listed Quality Factor. A good rutter can knock 5% off that time, provided it is accurate. For a ship's master familiar with the local conditions in such a vessel 10% might even be possible.
A poorly outfitted ship, without a gravscanner, or with an inferior one, traveling though unfamiliar subspace can easily make only half the usual quality factor, less if storms make areas of subspace impassible for a time.
It is also possible for local gravitational eddies to allow one vessel to outpace another. Experienced masters can often, by using sensor information from a gravscanner, ride these local eddies to gain an advantage in combat or trade. Such instabilities are rare along the groomed Major Routes or Highways, but rather more common off the grid.