Don't know all of the answers but here goes...
1. I'm running Pagestream 4.1 just fine on my Peg + MOS system. There was a few problems related to installation. However, there will be a MOS-native version of Pagestream and Grasshopper LLC is offering a cross-grade offer. I don't know about the other software mentionned.
2. I use Hyperion's Quake II and it works fine. I have to use software renderer since I'm currently on a Radeon though.
3. Never tried, can't tell.
4. Well, my Peg is leagues more stable then my A4000. At the moment the Peg is about as stable as the software your running... There are some bugs here and there, but I generally don't run into them.
Steph