The length of the double pointed needles doesn't really matter at all (unless you were knitting something huge like a sweater for big man, then you would need longer needles to hold all of the stitches). Just pick the size needles that give you the gauge you need. You can knit as few as 3 stitches in the round on dpns. Hope this helps.
Originally Posted by campingmumma
What length do you recommend for the F&F longies in the round - I have plenty of circular needles from doing the LTK pattern but I have no clue what double-pointeds I should get????