Set a lower clock speed, underclock and power limit in the Claymore bat/config e.g.

-cclock 1150,1150,1150,1150,1150
-mclock 2000,2000,2000,1900,2000
-powlim -10,-10,-10,-13,-15,-5
-cvddc 950,925,925,900,950
-mvddc 950,925,925,900,950

or use OverdriveNtool to create profiles for your cards as explained on www.mining.help.