When we speak of martial arts in the Jin Yong universe, DGSD is considered the peak of extremity. Specifically, when we speak of lightness kung fu, Duan Yu with his Treading Waves Lightness Steps is one of the most revered. And yet, I have found some evidence which implies that the best qing gong (hing gung) of DGSD may not be on par with the profound lightness kung fu of Reverend Kongjian from HSDS.
In DGSD, when Xuzhu tried to jump over a cliff (after receiving full strengths from 3 Xiaoyao Sect sages), it is written: 这五丈阔的深谷说宽不宽,但要一跃而过,却也非世间任何轻功所能。 Roughly: It is impossible for any lightness kung fu from this era to offer the ability the jump over a distance of 5 zhang (50 feet).
In HSDS, Reverend Kongjian dashed to a distance of 4 zhang away in a flash. Jin Yong used the term "floating" to describe this feat, so it sounds like Kongjian used one leap to reach a distance of 4 zhang.
So, DGSD's best lightness kung fu < 5 zhang
while Reverend Kongjian >= 4 zhang.
Clearly, this would imply that Kongjian (who may not have utilized his fullest lightness skills) is on par with the finest lightness leaper from the mightiest era (Duan Yu or Xuzhu).
Thanks, MisterM, for your excellent inspiration behind this discovery.