I have found the Sarcococca to be super slow to establish in dry shade, it is taking years (I have not watered them much) I love the smell of the flowers in late winter. Mine is about 7 years old, is now 12" x 12".
Tiarella for me wants some water, obviously struggles when too dry.
The absolute best and most rugged for dry shade that I have found is Epimedium pinnatum ssp colchicum (bright yellow flowers in spring) and Epimedium x warlyense (orange flowers in spring). The Epimedium experts warn that some of the newer fancy varieties are bred from the Chinese species, where it rains in summer so they are often less drought tolerant.
I am also having success, slowly, with Iris foetidissima var. lutea. Mine have yet to bloom, but have clearly established in dry shade. The blooms are not supposed to be very noteworthy, but the persistent red berries that are very showy.
