My two coppers: In the armor descriptions, you said they have "hasted" armor. I assume you're referring to the Speed enhancement from DotF. If so, although it hasn't officially been errated yet, the designers have figured out that Speed should not be a +3 enhancement, but instead a +7. That would allow you to re-engineer their armor, with a good excuse....just blame it on the designer!
Rust Monsters make effective armor and weapon destroyers, and the spell Rusting Grasp works well too (hint- since it's a 4th level spell, you can have a wand of it, negating the need to actually touch these powerhouses). The players can't gripe too much if they are stupid enough to smack a rust monster with that +10 weapon! Without the Everbright enhancement (MGoF), their armor and weapons don't stand much of a chance against a group of these metal-eaters.
Mord's Disjunction is the easy way out, but most players feel cheated that one spell nuked everything they own. From the SRD: "and permanent magic items must make successful Will saves or be turned into normal items. An item in a creature’s possession uses its own Will save bonus or its possessor’s Will save bonus, whichever is higher." IMO, with characters of this level, their items would most likely make the needed saves.