I hear ya. But PRUs are not really a good benchmark for that. This is the main reason why I don’t post power/speed/LPI settings. I found this out the hard way with @rebecca & @takitus. Our units are very much WIP (in a good way).
I’m guessing it’s because the head is moving to the extent/bounds of the artwork while it’s engraving (ie: raster mode). So if you had two items to produce, both identical artwork, but say one was scaled up 100% (ie: twice the size) and both ran at the same LPI setting, the larger one will take at least 2X as long because it has twice the number of scan lines the head has to travel, but may take up to 4X as long because it has 4X the surface area to print.
To answer your question about speed effects on engraving: darker, bigger, and higher resolution all take longer. There’s some basic physics there that doesn’t change.
Alignment is already better on production machines, and will continue to get much better in software over time. There are factory calibrations performed on production machines that will make them more capable than prerelease machines will ever be.