I have some designs that I made on the Chinese 60w(50) laser, and basically, I manually set the power and speed to the fastest possible to barely, but surely, get through in a single pass. As long as alignment is in order(almost perfect) the cuts go through in same uniform fashion from one sheet to the next.
To really do this comparison, we would need to put the same design through another laser and the glowforge, with the same material. We would be comparing mostly with speed at which we can achieve the same cuts in as least time as possible, with noting the power level.
But, this runs into another issue.
You can crank up power to 100% or even higher(not safe) and it’s going to be damaging to the life of the tube. There’s allegedly a sweet spot of amps driven through the tube that is “most cut power per amp” that is at the top of a bell curve around 60~70% in average Chinese laser.
The glowforge being awesome, may have those settings preset to prolong the life of the tube (and for overall safety) that it is going to output “x” burn power on certain material, and thus go at “y” speed.
The glowforge will have superior optics and focus, so we’ll assume it can do more with the output of its tube than the average Chinese laser.
I have a design I had cut on an 80w redsail. In 3mm acrylic, I could cut it at 90% power, at 18mm /sec.
Then I got my own 60w machine(with a 50w tube) and I wanted to be more careful with the tube so I cut at 70% power(closer to the top of bell curve) and 9 mm/sec. I have made the same cut at 50% power and 22 mm/sec on this machine.
Even though glowforge is a 40w tube, depending on %power being driven it will take less or more speed…
Which brings us back to, you can’t truly compare speeds unless you’re willing to dip into the power changes discussion.