I have not used that yarn, but my DK weight yarns generally are 24 stitches to 4 inches using size 5 needles and sports weight are 22 inches for 4 inches, but I would say swatch and use any yarn that gives you the correct weight. I think something slightly heavier than sports weight or use larger needles if it doesn't affect the drape of the garment. Try a swatch first.
Oh, after I originally posted this I found their site,
www.sullivans.net or their Australia siteBellaOnline ALERT: Raw URLs are not allowed in these forums for security reasons. Please use UBB code. If you don't know how to do UBB code just post here for help - we will help out!