Editing - Knowing when to stop

My editing is done for now, and my new novel The Gilded Lily, companion volume to The Lady's Slipper,  is with my agent. She has read it, loved it, and thinks it is ready to go off to the publishers. It has taken me over six months of editing, fiddling and re-writing to feel confident enough to send it to her, and even now there would be more work to do if I didn't decide to over-ride my over-active perfectionist and just stop somewhere.

So how did I know it was ready? I suppose the changes I...