I'd heat wrap my exhuast manifolds before I'd use this. With HP comes heat, and the ST simply doesn't make enough HP to drive the coolant temperature to a horsepower robbing temperature. I look at this as a higher-level type thing, when you've done almost everything else to make HP but are still coming up short, or need a more consistant coolant temp for more consistant times. I'd spend my money elsewhere.
BTW, that "20 °" is under ideal conditions on ideal motors, I'd be surprised to see this stuff actually drop the coolant temp in the ST any more then 8-10 degrees, which really doesn't amount to much. Any HP gain from that would quickly be eaten by the ac compressor, torque converter, or any other parasitic HP robber.