After our first round of quads, we wanted to try a few less popular versions, with mixed success:

• Kasteel Donker: Neither Wind nor I cared for this at all — it has an overwhelming black cherry flavor, and not much else going on.
• Malheur 12°: This was very nice, with a lot of spicy, almost peppery notes.  Definitely taking the typical abbey complexity and spiciness to an extreme, and I think it works well.
• Gulden Draak 9000: My favorite of the new brews, with a co2 bite and a boozy kick.  Uncharacteristically medium amber color.  Very smooth, clean flavor, in sharp contrast to the Malheur.  As with the tripels, these two are a very good example in contrasting takes on the style that both work well.

We also had a couple of favorites (including another bottle of St. Bernardus to replace a spoiled bottle from the first round):

• St. Bernardus Abt 12: An unspoiled bottle showed a wonderful complexity, with raisiny sweetness, spiciness, and earthiness.
• Rochefort 10: A clear favorite of this batch for both of us, with a big boozy kick, but blended perfectly with sweet malt and spiciness.

Overall, I think I found the quads to be a little less varied than the tripels, but still differing quite a bit (and differing in the same way as the tripels — with some being very boozy but otherwise mild, and others being more spicy and earthy).  The Kasteel Donker was the only beer in this group that I’d say was disappointing.  I still haven’t had them side-by-side, so I’d be hard pressed to pick a favorite among the Westy 12, St. Bernardus 12 and Rochefort 10.  I’d happily drink any of them any time.