Wendy, from reading your other posts it sounds as though you and I have exactly the same sort of questions!
I have the Gro Clock on order, should be here early Sept and I can't wait. That said, we managed to get 11hrs out of her last night, with wakings only at 3am (resettled really quickly), then 4.40am (bit of persuading, white noise and music before she resettled) and 5.20am (resettled herself after a few minutes of very loud Uh-Ohs and turning her music on!) and up for the day at 5.45am.
I've only been averaging 5 hrs broken sleep a night though as I'm getting a bit stressed lying awake waiting for her to wake up, as well as the new baby using my bladder as a trampoline all night, so things aren't very pretty from a pregnant, hormonal, overtired mummy point of view. I've actually called our local baby whisperer for an appointment on Thursday to see what she suggests. A friend who was also having probs with her 18month old is having huge success since seeing her, so fingers crossed!