Thanks for the notes on the Rieston! I figure that I'll just chat about the Armagnacs here.
Darroze really does a great job picking out barrels, but sometimes he gets to them a little late and they are over-oaked. I think that the woodiness, dryness, and strength in armagnacs really vary by the producer and location. I've had a few from producers in Le Frêche, and they have really peaked at around 30 years. My favorite spirit ever is a 30 year old Darroze Domaine de Salie (1979), which I subsequently sought globally. I'm about to take the plunge for some older ones, too, in the hope that they are not yet over-oaked. I had a 1972 Coquillon (also by Darroze, and also from Le Frêche) that was near 37 years old (if I recall) and it was a little looser and had a touch more wood, but still within bounds, and feeding my hope about the bottles of Salie. I had a 17 year old Salie from '94, and it was borderline stellar, and it's possible to get a sense of its greatness, but it does need just a bit more time.
I wonder whether armagnac from certain locations require slightly greater ageing than juice from other areas. With cognac, people say that Grande Champagne produces the best, most powerful cognac, but it is rough in its youth and needs more time than other places, like the Borderies. Generally, though, I think that 20 years is a pretty good point for the sweet spot (to avoid over-oaking and keeping a nice, high proof). It's definitely worth lots of comparisons! Another very solid armagnac house is 'Laberdolive.' I've had a few bottles of their stuff and found it solid.
It's great to hear from another armagnac aficionado! You're 100% on the mark about the explosive flavors in it. Darroze armagnacs compared to cognac reminds me, in some ways, of the difference between a George T Stagg bourbon (or W.L.Weller) compared to a Pappy 20. The cognac and Pappy are terrific and smooth, but the armagnac and Stagg can really blow you away.
Have you had the brut de fut Boujus?