Hello, Shelly---
Yes, there were two Scythias. (Actually there were four, but the last two were cargo carriers, not passenger ships.)
The first, the Lizzie Borden Scythia, served Cunard from 1875 until 1898. Until 1884, she was on the Liverpool-New York service; from 1884 on she served primarily on the Liverpool-Boston service. This Scythia was scrapped in 1899.
The second Scythia and Parthia can be found at
http://www.greatships.net/scythia2.html, and
http://www.greatships.net/parthia2.html, respectively. It's probably more accurate to call them "contemporaries" than "running mates" in the 50's, since Scythia sailed primarily to Canada in those years, while Parthia served New York.
Sources: Haws' Merchant Fleets; Bonsor's North Atlantic Seaway.
MAB