The OST gathers most transition scene BGMs indeed. Postmeridie is the best of them all, IMHO.
And the rest of the OST is pure classics - Sis Puella Magica, Salvae Terrae Magicae, Gradus Prohibitus, Credens Justitiam, Terror Adhaerens, Pugna cum Maga... And the second OST promises to have even more of such tracks. Overall (and it's sensible to discuss the OST overall, since it's basically one album split in half), this is easily landing among Kajiura's best works.
I'm sad that we don't get Sayaka's theme right now, but oh well. Come on Sony, make it July, with BD Vol 4!