I have finally received both HiFace back.
First thing I tried was listening both with 24/96 material. I used some available demo files from HD Tracks and 2L for that. I could also try later with a few rip i made of DVD-A at 24/192, but so far, I am unable to spot differences between both HiFaces at this sample rate. They just sound identical to me, which makes sense, since they are both relying on the same clock at 48khz mutliples. That is while playing on my main rig, Lavry DA11 and Beyer DT48A.
Second thing I tried was listening 44.1khz files with the "small clock" HiFace on a more forgiving system: Lavry DA11/LD mkIII/Sony CD900ST. Listenable I would describe it... It didn't strike me as bad as I remembered, when I could barley listen to music for more than 5 minutes. The tube colorations in a certain way masked the poor timing of the music. However, switching back to the "large clock" HiFace was a revelation, even on this system. Much better mids, voices fuller and richer, a much better sense of pace and rithm, much better articulation (so apparent on voices), soundstage suddenly opens and images precisely.
So while not as extreme as my first experience with the small clocks HiFace, I can say with confidence that even on a not so resolving system, differences still exists. But I understand how they could be tolerable for some, and maybe why people haven't been complaining that much untill now... Just a guess though.