Are all the IMAX 3D showings 48 FPS?
The IMAX version showing in Pittsburgh, PA is at "Cinemark Galleria at Pittsburgh Mills and IMAX" and it only lists "IMAX 3D", "RealD 3D" and "Digital Cinema 2D". I assume the Digital Cinema 2D and RealD 2D are going to be 24 FPS versions. From the listing it also seems the IMAX 3D is going to be 24 FPS as well.
This theater is not in the list at
http://www.thehobbit.com/hfr3d/ or any of the other sources I could find.
The other theater in Pittsburgh, "Cinemark Robinson Township and XD" does have a listing for "Cinemark XD High Frame Rate - RealD 3D"