@Niels_Dekker as you have noted and Terry Mahaffey notes in the reply, the behavior depends on the specific situation and the compiler. And, in many cases, the compiler can infer whether exception-related optimizations are possible or not.
@jhlegarreta and I are working towards a GitHub check that will show performance differences across the different platforms and compilers.
Once we have the check in place, we will be able to determine 1., 2., and 3. We have observed that behavior varies vastly across compliers sometimes. Once we have performance testing, we could add the specification for 1. remove it for ‘2.’ and ‘*3.’ If we find that Visual Studio just has issues in some cases where the other compilers see a performance increase, we could define ITK_NOEXCEPT to be empty with Visual Studio. Where it always demonstrates peformance improvements, we could use noexcept.
Until then, ITK_NOEXCEPT serves a useful, grep’able marker that is still functional.