Ok, so i didn't go with proper curtains because i couldnt find any that insulated as well as i wanted for the price i wanted. And i havent worked out how to sew my own yet; so i came up with a curtain alternative that has worked ok so far.
The insulating layer closest to the window is polar fleece - a single layer with cafe clips, or a double layer simply folded over the curtain rod for extra insulation trapping the air in between the layers.
A bonus was that polar fleece worked out to be almost a total blackout curtain, and was quite cheap - less than $10 per metre.
The outer layer of a nice organza is to trap more air and to have a translucent layer to allow light in in the daytime. - and to look nice in the evening rather than looking at polar fleece. You may have guessed I like rich colours, so mine are purple and magenta, but in the flat next door I used a demure coffee cream combination.
Now (for you scientific types) measure the temperature again with pelmets and curtains to see how much they improve the internal climate of your house, and let me know if they make a difference. Mine did by about 2 to 3 degrees, meaning i can turn the heater down and save electricity...
Another thing you might want to do with your pelmets is to cover them with fabric to match your curtains, but i like the clean lines of these as they are. I imagine you could also fashion them more decoratively, or use a decorative molding or painted finish to complement the style of your home if you felt so inclined.