Just to add some data points to this particular graph (mostly for my own interest):
http://img34.exs.cx/img34/5439/nexxus-mcw6000-temps.gif
White Water
Eheim 1046 = 14.21
Eheim 1048 = 13.49
Eheim 1250 = 13.14
MCP600 = 13.02
MCP650 = 13.16
Cascade
Eheim 1046 = 13.74
Eheim 1048 = 13.17
Eheim 1250 = 13.02
MCP600 = 12.86
MCP650 = 13.04
Storm/G4
Eheim 1046 = 13.71
Eheim 1048 = 12.98
Eheim 1250 = 12.74
MCP600 = 12.43
MCP650 = 12.77
Storm/G5
Eheim 1046 = 13.25
Eheim 1048 = 12.62
Eheim 1250 = 12.18
MCP600 = 11.78
MCP650 = 12.17