Since you're using 5.005, why not try 5.6.1 first? 5.6.1 is very stable and reliable. You can always keep multiple versions of Perl by putting them in separate directories.
One important note, 5.8 and 5.6.1 are not binary compatible. So, many Perl modules available to 5.6.1 might not be available to 5.8.
The bottom line is, just put different versions of Perl in different directories, try them all out, judge for yourself.