As you were messing around the area where the new drywall butts up to
the old ceiling, does the acoustical texturing want to come off easily?
If so, remove enough to tape and mud, then re-texture the new ceiling
blending the new texturing on to the existing.
Alternatively, you could remove all the acoustical texturing,
re-texture the whole ceiling. DAGS in the news groups, lots of
information on removing texturing...