I would vote on which 1 is faster.
I generally think using a custom identifier is slower.
Suppose I made a custom identifier $calculate() based exactly on $calc().
If I used something like.
alias calculate { return $calc($1-) }
I guess the question is is making a non-custom identifier any negligibly faster than using a custom identifier.
For the $iseven or $isodd case, probably not.
And since there's so many ways to check for $iseven or $isodd, I would say a default identifier would have to be slower than using a simple custom identifier (especially if Khaled combined all the above examples in his C++ source for such an identifier).
So probably meaningless.
-Neal.