My run of the test on perl-5.10.1 (linux-amd64) confirms cromatics' findings:

luben@karavelov:~/perl$ ./t -N=4000
4000: Took 2.062 seconds
luben@karavelov:~/perl$ ./tac -N=4000
4000: Took 2.538 seconds
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And the perl version:

luben@karavelov:~/perl$ perl -V
Summary of my perl5 (revision 5 version 10 subversion 1) configuration
+:
   
  Platform:
    osname=linux, osvers=2.6.32-trunk-amd64, archname=x86_64-linux-gnu
+-thread-multi
    uname='linux madeleine 2.6.32-trunk-amd64 #1 smp sun jan 10 22:40:
+40 utc 2010 x86_64 gnulinux '
    config_args='-Dusethreads -Duselargefiles -Dccflags=-DDEBIAN -Dccc
+dlflags=-fPIC -Darchname=x86_64-linux-gnu -Dprefix=/usr -Dprivlib=/us
+r/share/perl/5.10 -Darchlib=/usr/lib/perl/5.10 -Dvendorprefix=/usr -D
+vendorlib=/usr/share/perl5 -Dvendorarch=/usr/lib/perl5 -Dsiteprefix=/
+usr/local -Dsitelib=/usr/local/share/perl/5.10.1 -Dsitearch=/usr/loca
+l/lib/perl/5.10.1 -Dman1dir=/usr/share/man/man1 -Dman3dir=/usr/share/
+man/man3 -Dsiteman1dir=/usr/local/man/man1 -Dsiteman3dir=/usr/local/m
+an/man3 -Dman1ext=1 -Dman3ext=3perl -Dpager=/usr/bin/sensible-pager -
+Uafs -Ud_csh -Ud_ualarm -Uusesfio -Uusenm -DDEBUGGING=-g -Doptimize=-
+O2 -Duseshrplib -Dlibperl=libperl.so.5.10.1 -Dd_dosuid -des'
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=define, usemultiplicity=define
    useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=und
+ef
    use64bitint=define, use64bitall=define, uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  ...
Characteristics of this binary (from libperl): 
  Compile-time options: MULTIPLICITY PERL_DONT_CREATE_GVSV
                        PERL_IMPLICIT_CONTEXT PERL_MALLOC_WRAP USE_64_
+BIT_ALL
                        USE_64_BIT_INT USE_ITHREADS USE_LARGE_FILES
                        USE_PERLIO USE_REENTRANT_API
...
[download]

The versions of autobox and autobox::Core are the same as yours. May be it is a problem with the windows version of perl.