YES, do it. Lester will get you the Ks you need. Cain is solid with a low ERA, but doesn't get as much run support.
Help me please: viewtopic.php?f=26&t=385729
OF: Ethier, Jennings, Willingham, Quentin
BN: De Aza, Pagan, Aviles
P: Felix, Price, Buchholz, Lynne, J. Johnson, Wandy, Valverde, Jansen, Chapman, Betancourt