Agree with the last post, friend of mine has a Empire resurrection and its a handsome beast.
Think its runs on low pressure so it should cover your requirement for efficient use of air.
Haven’t seen too many selling second hand though :S
GOG Enemy, simpler, probably cheaper than a mag or cocker and at least as efficient as the mag. I love cockers but they're heavy and overly complicated.
Agree I have both and the enmey is a really simple marker that is light and works with only a little maintenance. Ion thread barrel is the only downside.