I'd say 4k, as that is scanning range for IDs. It gives room for bombers to manouver, and allows capitals to blast each other at range.
Edge, you only need to be 2k away from the capital to dodge its fire. If its a cruiser/battleship, you can also sit there strafing and supernovaing. That's legal, and won't result in any "you fled!" reports.
Quote:No cruise by any means. If you can't catch a fighter with a GB, too bad.
Get a fighter and chase him.
I must concur with Chopper's statement, this clearly sums up the cruise rule.