Managed to increase speed by performing binary search on @keys. My module is now only about 40% slower when max_items=100 and 4x slower when max_items=1000.

package Data::Throttler_CHI;

use strict;
use warnings;

use List::BinarySearch::XS qw(binsearch_pos);

sub new {
    my ($package, %args) = @_;
    bless \%args, $package;
}

my $counter = 0;
sub try_push {
    my $self = shift;
    my $now = time();
    $counter++;
    $counter = 0 if $counter == 2e31; # wraparound 32bit int
    $self->{cache}->set(sprintf("%010d %d", $now, $counter), 1, $self-
+>{interval}); # Y2286!

    # we assume the driver returns keys in insert order, to avoid havi
+ng to sort()
    #my @keys = sort $self->{cache}->get_keys;
    my @keys = $self->{cache}->get_keys;

    return 1 if @keys <= $self->{max_items};

    my $time_expired = $now - $self->{interval};
    my $pos_not_expired = binsearch_pos { no warnings 'numeric'; $a <=
+> $b } $time_expired, @keys;

    $self->{cache}->purge if rand() < 0.01;

    (@keys - $pos_not_expired) <= $self->{max_items} ? 1:0;
}

1;
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