Ok so we know that Dugu reached the No Sword stage, whether he mastered it or not is up for grabs.
We also know that Yang Guo reached the Wooden Sword stage, but didn't master it.
Now we know with the HIS pre-16 Years he is stronger than GWM in pure fighting, but not inner strength.
When he clashed with his metal sword against GWM 16 years later, he was surprised that he was only equal to GWM.
Now unless Yang Guo is a moron and assumes GWM didn't improve in 16 years, this indicates that he improved a great deal in pure inner strength, and that the power he generated must be much greater than the HIS. He couldn't win a clash 16 years ago with the HIS, and now against a much stronger GWM, he is surprised he did not win. The power he generated with the metal sword in that incident must be around 1.5x the power he generated with the HIS. Of course if he had the HIS he would have been even more powerful, but that's not important for now.
So by improving to the Wooden Sword level, he has increased his power by roughly 50% if we guesstimate. Feel free to disagree. If he gave up on the Wooden Sword stage and stopped trying to master it, I think it's logical to say that it is not only harder to master it than to reach it, but it would also yield greater benefits than merely reaching it. If we increase his power again by 50% if he masters Wooden Sword, and another 50% if he reaches No Sword but doesn't master it, he would in total be at least twice as powerful as the Greats.
The numbers are variable and just my guesstimates, but I would like for anyone to point out any flaws in my logic. The important point is that Yang Guo is not dumb enough to assume GWM will not improve over 16 years, and that he is surprised he did not win the sword clash easily. This indicates that the power he generated with the metal sword should be at least 150% of what he was able to generate 16 years ago with the HIS, and that reaching a new level of Dugu's art roughly equates to his proportionate increase in power.