I thought I'd report in on my little experiment. Very interesting excercise and one well worth repeating! I kept on feeding when the SG got down to 1000 or thereabouts with 50g dextrose. When the SG didn't fall anymore after adding the sugar, I stoped, added stabiliser, finings etc. When clear, bottled into half wine bottles. Knowing when it was clear was a problem though, it's so dark that I had to use a very bright torch! It looks realy good in the glass!
For my taste, it tastes a bit too much of elderberry, I like elderberry but I feel this is a bit too much. SWMBO likes it but wants even more sweetener than me, so I'm only sweetening at point of use. When sweetened it has a really good mouthfeel and I'm really glad I bottled in half bottles or we'd have to drink more each time.
A receipe well worth repeating on the whole. I think I'd reduce the Elderberries to half and now that I've settled back into the whole wine making process, I'll be "logging" the SG more. This is the joy of homebrew, try it, learn something new, and so far make some really nice stuff!