Thanks for the info, David.
Unfortunately the BPMs are going to fluctuate throughout the project on a cue by cue basis.
At my current BPM settings I'm at a maximum of 15,765 measures at SMPTE time 13:00:00:00. The BPMs have shifted a couple of times as I've worked on new cues, and it seems that the 13 hour mark is what's defining the limit (rather than the number of measures).
It's kind of unfortunate that Logic even builds in this kind of limitation. I know that most projects won't be this long, but it seems like some arbitrary limit was just chosen. Perhaps there's a hidden technical reason to limit project lengths, but it's kind of frustrating when you run into what seems like an unnecessary wall.
Anyway, thanks again for the response.