Thanks, Tom. I never looked into acros after giving up on TMX and moving back to traditional emulsions. But with those kind of reciprocity characteristics, I'll have to order a box and see how it performs.
On my original question, after reading almost everything available on the usual photo-chat sites, I've come to the conclusion that my notion of film becoming "desensitized" during extended exposures was pretty silly. It's a relief of sorts -- who needed another variable to battle?