I got mine done by birds at 87k miles ish.
Apparently they weren't too bad, probably due to a lot of motorway miles and comparatively few short trip driving. Meth and oil catch can were fitted too recently to make a difference.
I hear every 50k miles is a reasonably interval for cleaning. I probably won't keep mine that long, on 95k now.
Car: 2010 Jaguar XFR (Cat-back exhaust)
Gone but not forgotten: Highly Modified E90 335i LCI M Sport Manual (circa 480BHP/500lb ft)