Gorgeous trains, really! I think they are the prettiest Shinkansen trains, along with the E7 / W7 and the 500 series. May they have a long, happy career on the rails.
According to this website, the Tsubasa, which departs from Tokyo Station at 5pm, is scheduled to use the E8 series :) www.jreast.co.jp/sendai/yamagata_e8_debut/