Oh, you meant runtime performance! Sorry, I completely failed to recognize that. I thought you meant the clunkiness of Perl 5 subroutine argument processing:
my ($foo, $bar, $baz); # oops, forgot " = @_"
my ($foo, $bar, $baz) = shift; # oops, used shift() instead of
my $single_arg = @_; # oops, will usually be 1
Perl6::Declare lets you declare subroutine/methods using Perl 6 signatures, which are lovely. I heard this turns out to actually be faster than Perl 5 calling conventions, but I can't say I fully understand why this is so.