I just added a tip to the Wiki:
I don’t know if this will always be true, but if you have a design that has a lot of engraving, orient the bulk of the engraving in the horizontal direction in the GFUI. I just tried a design that was about height:width of 3:1, and if engraved in a vertical orientation it would have taken 27:15 minutes whereas if rotated 90 degrees the time was 19:36. No other changes. This was a vector engrave. May not be true of raster engraves.