Yes th Angliru is an absolute nightmare. There is a climb very similar but shorter on te east coast of Spain which sits at 25-27%. The minimum you need to spin up is a 39_27 if you are a STRONG climber.
Also near Santander there is a climb we did a TT up last spring. My friend lent me his rear nucleon wheel cos it had a 25 on it and I just had a 23. This was about 25% for about 5-6km.
I drove up the Angliru in a 4x4 back in 2000. We had trobule getting up it. It normally rains in that regio about 6 months of the year so you can imagine riding a road bike up with the back wheel slipping.
If I had to TT the Angliru I would sling on a 50-36 and slap on a cassette which had anything as a big as a 30 or 32 on it. The Angliru is exceptional but the idea of this thread is to find the most useful set up for the aerage rider adn for me the 50-36 mated to an 11-23 just about gets it.