Definitly 560 (Dx11+faster+better scaling in SLI+Better temps+lower noice).
Its more expensive yes, but Id never advice you to get something getting "outdated".
460 will hold for 1 year more probably, but not that much longer.
Also note that so far DX12 oficiall resease is 2013 (1 year after worlds end
), and in 2 years i guess you will be able to update for new GPU