Even stranger, cos I'm using AS1004 also. The only difference is that I'm using the 64-bit version:

c:\test>perl -V
Summary of my perl5 (revision 5 version 10 subversion 0) configuration
+:
  Platform:
    osname=MSWin32, osvers=5.2, archname=MSWin32-x64-multi-thread
...
Characteristics of this binary (from libperl):
  Compile-time options: MULTIPLICITY PERL_DONT_CREATE_GVSV
                        PERL_IMPLICIT_CONTEXT PERL_IMPLICIT_SYS
                        PERL_MALLOC_WRAP PL_OP_SLAB_ALLOC USE_64_BIT_I
+NT
                        USE_ITHREADS USE_LARGE_FILES USE_PERLIO
                        USE_SITECUSTOMIZE
  Locally applied patches:
        ActivePerl Build 1004 [287188]
        33741 avoids segfaults invoking S_raise_signal() (on Linux)
        33763 Win32 process ids can have more than 16 bits
        32809 Load 'loadable object' with non-default file extension
        32728 64-bit fix for Time::Local
  Built under MSWin32
  Compiled at Sep  3 2008 12:22:07
  @INC:
    C:/Perl64/site/lib
    C:/Perl64/lib
    .
[download]

And I don't see the problem with 5.8.9/32-bit either:

c:\test>\perl32\bin\perl5.8.9.exe junk.pl
Records: 400000 in 6.732 seconds
Records: 300000 in 4.329 seconds
Records: 400000 in 4.537 seconds
Records: 300000 in 3.365 seconds
Records: 400000 in 4.495 seconds
[download]

I think you should look closer at what is going on there. (I'll try to grab a copy of AS1004 32-bit and run it for comparison purposes.)

The -V of my ASPerl:

d:\Web-Dev\arrays>perl -V
Summary of my perl5 (revision 5 version 10 subversion 0) configuration
+:
  Platform:
    osname=MSWin32, osvers=5.00, archname=MSWin32-x86-multi-thread

Characteristics of this binary (from libperl):
  Compile-time options: MULTIPLICITY PERL_DONT_CREATE_GVSV
                        PERL_IMPLICIT_CONTEXT PERL_IMPLICIT_SYS
                        PERL_MALLOC_WRAP PL_OP_SLAB_ALLOC USE_ITHREADS
                        USE_LARGE_FILES USE_PERLIO USE_SITECUSTOMIZE
  Locally applied patches:
        ActivePerl Build 1004 [287188]
        33741 avoids segfaults invoking S_raise_signal() (on Linux)
        33763 Win32 process ids can have more than 16 bits
        32809 Load 'loadable object' with non-default file extension
        32728 64-bit fix for Time::Local
  Built under MSWin32
  Compiled at Sep  3 2008 13:16:37
  @INC:
    C:/Perl/site/lib
    C:/Perl/lib
    .
[download]

I'm not sure as to how i can look closer here. Suggestions as to what tests i can run are welcome. Meanwhile, here's snapshots of both, done with Procmon and NYTProf: http://drop.io/perl_performance

Suggestions as to what tests i can run are welcome.

The profiling you've done doesn't get into enough detail in the critical areas.

The first thing I would try, is isolating whether the extra time is spent reading from the file or shuffling memory. To that end, I'd see what happens to the timings if I just read the data but didn't store it:

#! perl -slw
#use 5.010;
use strict;
use Time::HiRes qw[ time ];;

sub x{
    open my $fh, '<', shift or die $!;
#    my @AoA;
    my $dummy = [ split ',' ] while <$fh>;
    close $fh;
    return $.;
}

for ( 1 .. 5 ) {
    my $start = time;
    printf "Records: %d in %.3f seconds\n",
        x( sprintf 'junk%d.dat', 1+ ($_ & 1) ),
        time() - $start;
}
[download]

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