When I did my first rack of baby backs I used the 321 @250ish. They came out great. It was in my UDS with a diffuser.
Keep in mind that I could mimic someone in Texas and have different results because of a number of variables. Elevation, humidity, the meat it's self.
I'd check it every 15 from the 3hr mark. Ultimately the bend test will produce the best consistancy like the probe on brisket and the bone pulling out of a Butt. Temp and time are nothing more than a guideline as to when to check your meat.
UDS (not so U) UDD, 22.5 OTS, Coming soon: mini UDS & double barreled RFS