I wouldn't say strength and life of the struts are  related particularly.
or stated another way, I sure would not want to wait 5 years for an extra
strong one to be about right finally. And besides, it would be near the end
of its life then anyway.
but you sure do not want too strong ones ......
that makes it way too hard to close.
What I do is order 'the medium one' .
Then I test how much strength is left in each strut, and replace the weaker
one.  That often turns out quite nicely.
then I write the date on the one I just installed, so next time I know which
one is the older more-worn-out one.
works for me.

on rare occasion, I've had to juggle struts between two or 3 vans to get all
2 or 3 rear hatches that stay up nicely, and aren't too hard to close
either.
Scott
www.turbovans.com

---- Original Message -----
From: "Edward Maglott" <emaglott@BUNCOMBE.MAIN.NC.US>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Saturday, July 25, 2009 3:35 PM
Subject: hatch struts: 2 strong ones or 1?

>I don't intend to put a rack on my back hatch.  I've read that 2
> strong ones can make the hatch fly up when you open it.  I've read
> that one strong and one weak will let you leave the hatch partly open
> and it will stay.  I've read that 2 strong ones last longer than one
> of each.  Is all that true?
>
> Thanks,
> Edward