Hi,
You might find some useful info here:
http://www.endot.com/support/installation.asp
The 100 psi is a working pressure rating, and there is quite a bit of margin over that for water hammer etc. I belive they say at the link that they test each batch to 2.5 times working pressure.
I'm not sure how you would evaluate resistance to tree falls and the like -- maybe get a short section of each and see what it takes to bend/break them?
If the pipe is going to be exposed on the ground, then I would be bit concerned that where it passes through areas in direct sun that it would heat up some. The pressure rating they provide is at 73F, and it drops off as you go up. This won't be a problem when the water is flowing, since the water will cool the pipe, but if the flow stops and the pipe stays full, things could warm up, and it would still be under pressure. There is a temperature vs pressure chart in one of the docs at the link. Allowing a little bit of water to run all the time would keep it cool. The sun will also shorten the life of the pipe even if it has the UV stabalizers and carbon black pigment.
Gary