Lots of internet stories out there. There is no one stead fast rule that works when it comes to running cooler. Let's for a moment think about what really happens in a running engine. Fuel and O2 are burned in the cylinder and the expansion from that burn is pushing the piston downward. It is really all that counts. The bigger the fire the more power you produce. So if you increase power you have to increase the heat, there is no way around it. Now how much of the heat that comes from the cylinder do you feel? If you try to increase the amount of O2 entering the cylinder which is what you are doing when you change the camshaft, port the heads, ect. you are trying to increase power output and therefor are also increasing the heat produced. Now changing the exhaust to try and get the heat produced out and away from the engine does not reduce the amount produced, it just attempts to move it away sooner. The only issue on a HD is you sit very close to the exhaust pipes so you feel all that heat on your right leg. Some pipe designs get the pipes closer and some further away but the heat is still the same coming from the engine. A typical HD engine produces about 950 deg exhaust temperature at idle and about 1400 deg under load, so one has to ask themselves how close to you do you want all that heat and is that worse than a 250 deg engine?