That would be an awfully loose knit to use sockweight on a size 8 needle, unless it's a UK pattern and uses the old UK sizes which are the same as a US6/4mm. A size 4 US needle is a 3.5mm and a little small for a DK, so make sure you're reading those needles correctly. I would just try it with the size 6/4mm and see what gauge you get. It would help if you can link to the pattern or information about it to make sure you're reading the needle info correctly.
sue- knitting heretic