<p>On my Mac I've got two versions of Cura installed, in <code>/Applications/Cura250</code> and <code>/Applications/Cura262</code>.</p>

<p>How can I copy my printer and profile settings from Cura 2.5 to Cura 2.6?</p>

Generally speaking, the typical algorithm takes into account the slicer's speed settings for specific features of the build, such as infill, perimeters, top/bottom layers, etc. The distance traveled by the nozzle at a specific speed for each feature is also part of the equations involved. There are some rather vague portions of the nozzle movement based on acceleration and other factors which makes the calculations less accurate.
How accurate is it?
Not too accurate. My experience with three different slicers is that it's never been within better than ten percent. I believe the various combinations of features of a build are not going to be identical from one model to the next, preventing even a ballpark figure to be created from previous builds.