>Continuing and waiting for a config that requires 21 turns, dik

here's a pattern to try:
first do 6 checkerboards of order 2 (F2 B2 R2 L2 U2 D2) and then do
superfliptwist. in other words, the group product of these two elements.

As they commute I did it the other way around. But I am highly
suspicious that you tried it yourself. 10 minutes and only down
to 22 turns. But continuing, possibly for weeks/months.

On another machine I am trying to prove that 20 is minimal for
superfliptwist. 90 hours gone, still nothing. Most of the time
is not spend with phase 1 set to 16 turns. Phase 1 to 13 got it
doen to 20. Nothing new with phase 1 to 14 or 15. 16 turns in
phase 1 allows at most 3 turns in phase 2. The latter can be time
consuming. I do not know in how many cases actually something is
done in phase 2. When I get to 17 turns in phase 1, I suspect in
most cases in phase 2 it is immediately clear that it can not be
solved. But I am patient.

dik