If the 6.5 is run at the conservative power levels that GM sold them at they will be fine.

When the boost is elevated and the power level is jacked up the piston skirts can seaze due to the heat that is created by the extra boost.
The oil coolers are a necessary item on these engines but even with the sprayers will not take away enough of the heat to help.

The drop in the comp ratio to 18:1 drastically lowers the flame temperture during operation and allows the boost and fuel values to be bumped up a bunch.

For most applications the stock ratio is fine. Now when you get hungry and are not content with 10-12 PSI max and start wanting to run 15-20 PSI and have plans for this little creature to really rotate the earth then the 18:1 and an intercooler is a must have.

EGT above 1000f is not good.
All this heat has to go somewhere and the block, heads, valves and pistons take a horrible beating and soon something will fail.

Bt reducing the comp ratio the power levels can be bumped up into the 300hp range in a truck. The issue is still heat but its whats in the radiator now thats the worry.
In marine applications there is not issue as the pond is full of cool water and the engine temp can be easily controlled as can the inlet air temps using a water cooled charge cooler.

Heat is the big enemy here no matter how you cut it.

18:1 is a nice way to go if you are looking to make big power and then use it to reef on something real heavy.

Hope this helps

Robyn