Cook 1 cup rye berries in simmering salted water until tender, about 1 hour. Drain, transfer to a bowl and let cool. Add 1 cup each thinly sliced red cabbage and celery and 1/2 cup chopped pastrami. Whisk 3 tablespoons each cider vinegar and whole-grain mustard and 1/3 cup olive oil; toss with the rye berry mixture. Season with salt and pepper.