Yarn Diving

I have one skein of Rowan Scottish Tweed DK. Three or four skeins of gorgeous Alice Starmore Hebrides 3-ply. They are not on the way to becoming a sweater.

What would happen if I tried something like this from the Jamieson's website? It takes the concept of making a warm shawl to the nth degree.

If you've tried a lace shawl in an aran or DK weight yarn, maybe you could give me a hint about needle size. The Jamieson's site suggests using a size 5 or 6 needle with the Aran weight.