this is what i do when installing a new perl version and want to retain the old one: suppose i have perl 5.8 installed in c:\perl , now when i want to install perl 5.10, first i rename c:\perl to c:\perl58, then installing 5.10 as usual to c:\perl , and when i want to use the old 5.8 i rename the new c:\perl to c:\perl510 and c:\perl58 to c:\perl , and if i want to install strawberry, rename first the activestate perl to perl510 and perl58 then install strawberry, now if you want to use perl 510 rename strawberry to something like strawberry512 and perl510 to perl. the same if you want to install camelbox to enjoy its Gtk2. this is a successfull approach, i am using it from long time ago.
so this way you will not bother of what is the first in the Path, because you have renamed the folders you do not want to access now but the strawberry folder as an example
my path like this:
c:\perl\site\bin;c:\perl\bin;c:\strawberry\c\bin;c:\strawberry\perl\bin;C:\camelbox;C:\camelbox\bin;
the only restriction is the ENV variables which a few modules may use.
and we can automate this naming and renaming using Bat files.