1) I don't know why everyone dogs on Sensi. COPS was a so so system, no question about it. Had to be set up right, and very few people took the time to learn how to do it and so they decided the entire thing was crap. I keep hearing everyone talking about "properly setting up" Sensi, but Sensi automatically sets itself up upon you shooting your first 10 or so shots... not exactly a difficult or strenuous task. I'm on Sensi and a HALO and never had a problem at all. With the 4's dual detents and bolt, most HALO's should work with it. As for HALO's pushing balls into the Sensi rod and the rod puncturing them? HA. Even if that EVER happened, the much more likey scenerio would be that the Sensi rod get's pushed down into the sensor and breaks it, not punctures the ball. HALO's didn't work with previous angels mostly because of the breach/bolt design and the single ball detent (evidenced by the fact that alot of LCD's have HALO trouble as well, and are free of eyes or a Sensi rod). Sensi may not be hip anymore, but it's not a bad system. Not to mention, no ugly chunks of metal and wires hanging off the side of an otherwise smooth marker.
2) Refer to above, I know nothing about it.
3) I know more than a couple people did it at angel-owners.com, but I mystified as to why and never bothered to read about it, so you'd have to go there and find out yourself.
4) ^^ .689
5) Silly question, everyone knows the Angel is the most maintenence free paint slinger out there.
6) I can only get 3000 psi fills around here, but with my 68 4500 filled only to 3000 I get a full HALO and my whole pack of pods (6) with some to spare.
If you buy anything else you'll wish you hadn't.