Lag in the v6 editor is a known issue, yes, and there's nothing that can be done about it on your end. I would prefer to keep a part around the 2000 frame mark and would be strongly discouraged from going above 3000 frames.
It's possible that changes to how AAO works could kill the lag, but I would need much more time to investigate.
[D]isordered speech is not so much injury to the lips that give it forth, as to the disproportion and incoherence of things in themselves, so negligently expressed. ~ Ben Jonson
Current AAO Development Priority: Issue #94: Grayscale Mode