>perl -MO=Deparse -e "my $check = ($y eq $z);my $check = $y eq $z;"
my $check = $y eq $z;
my $check = $y eq $z;
-e syntax OK
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Also, if Perl really were creating a one-element list, that one-element list would be true even if it only contained one undef element:

> perl -wle "my @hypothetical = (1 == 0); my $check = @hypothetical; p
+rint $check"
1
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So, Perl knows an expression when it sees one, and the expression is a simple boolean result, and nothing complicated.

Mostly though, if you are worrying about such minuscule optimizations, you should either be using C or spend the time about rethinking your approach to the problem, possibly either reworking your algorithms or reworking your data structures. In both, you'll find far more possibilities to speed up your program than in musings about how Perl evaluates boolean expressions.