That's impossible to determine until the suituation requiring such decisions occurs. Kind of like soldiers going into battle - not odd for the "real macho men" to lose it ans the apparent Harvey Milquetoast guys to perform some really heroic deeds.
If you want "proof" you're SOL for now. You might also ask, "Who do we have that we can be certain about in this area?" Let me know if you have a name that might meet the criteria.
IMHO, Palin has shown signs of the ability/willingness, and despite what we keep hearing about Perry, he has the potential.
We can be certain that in a decade long career as Governor, Perry has had many opportunities to make the hard choices. To put principle above politics.
The idea that he has not had these opportunities, again and again, is an impossibility.
The name I will give you is the name you already mention—Palin. What did she have to gain when she blew the whistle on Randy Ruedrich? Nothing but principle. What did she have to lose? Money, lots of it, and political power.
Palin chose to go with principle.