A full- bed engrave using the new “improved” SD engrave settings takes ~6hrs - that’s for an 18.99x10.97 image. 10.97*270(lpi)=2960 passes that take ~8 seconds each. No way around it. As you’ve seen, you can’t just drop the resolution as it messes up image quality.
The old SD settings take 3 hrs - but you’re limited to 18" width due to the higher speed (1000 vs 535)…