Just an update about my latest experiment with a set of d'Addario pro arte ej46FF. These are hard (well, quite hard) tension carbon and very thin strings. I tuned my Gretsch guitalele to F, and it appears to be a perfect match : the instrument really "sings" and keeps in tune, and this low pitch gives the feel of low to medium tension under the fingers. Incredible amount of volume and sustain. Much better than blue Alliance and Cantiga, maybe because the thinner gauge results in a much better intonation...
Guess the sound improvement must be astonishing on the laminate Yamaha GL1 as well.