If you want to support CS5, you have to use that version, otherwise you
risk writing commands that won't work in CS5.
Just remember to target the right version at the beginning of the script
so that it works on later versions too (and make sure to switch it back
to the proper scripting version with a finally statement at the end!)
What is the Object Model version for CS5?
CS5 = 7.0
Be aware that in your screenshots, you're just selecting what version Help is showing. In your script itself, you want to actually change the scripting engine, or (since there aren't SO many changes), don't change the engine, but just be careful to only use commands that are shared between all versions. I think there's a thread or two here on the forum listing the main differences between the DOMS of CS5 and later.