But the idea that warp factor X would give a significantly higher speed along a specific "space lane" is to be treated with utmost caution, because if the speed advantage offered by an "express lane" truly is significant, then this should be reflected in dialogue big time. No more dabbling in "warp factors" - the valiant skipper should be solely concerned with the question "Where is the nearest express lane?".
To be somewhat pedantic, "warp factor" would seem to be some sort of function of the engines' warping of space around the ship, not necessarily correlating to speed. We can probably assume the warping is more or less constant, but we can't say what speed that would give us. Just like the RPM's of the engine of a car don't tell us how fast we're going, it's the RPM's of the tires (assuming correct size and no slipping, of course); different conditions - gear ratio of the transmission, resistance against the tire turning, weight, etc. - will correlate to different speeds.
An aside - if we're only going to stick with what we see on-screen, Trek Tech would be pretty slow