Do the warp9 and you will fully understand how important the "clean treble" is. It is ear fatiguing after listening if the sound is very direct and not clean.
Yes, the Sheffield Wagner can be almost unlistenable unless treble is tip-top best. I was surprised it sounded as good as it did on your system.
Finding excellent stereo Wagner recordings in NM condition is difficult. There are LPs with snippets and movements but complete pieces such as Lohengrin or Siegfried are difficult. If you want power, conflict and death - big full bore hammer smashing yet beautiful as only Wagner can do - try 'Siegfried's Funeral March' from Twilight of the Gods. If you want gorgeous tippy-topmost trebled - higher than R.Strauss in Zarathustra - try Prelude To Act I From Lohengrin and then the Lohengrin Bridal March with wonderful chorus.
Tang, I am so happy to find you are exploring big orchestral music, late 19th-early 20thC, because your system can do it so well. You set a goal. Video is video but I get a chance to hear what is possible with some of the music I really enjoy.