I just uploaded this video and was amazed for about the 20th time as I listened to it. Grand Russian Fantasy (Jules Levy) is a solo I have played several times. The final variation is all triple tonguing (although there is an ossia option that is all arpeggios). Clarke zips through that triple tonguing at a tempo of about 140 for each double triplet! I think I have approached or gotten to 120 on my best day, but...wow!
My grad school teacher told to keep my tongue closer to the front of my mouth as I was triple tonguing. That means it has to cover less distance with each strike and gives a bit more speed. That works, but I don't know if a euphonium can get to this speed (especially on modern large horns and mouthpieces). What do you think?
https://www.youtube.com/watch?v=n0r-I_-ILQ8