Sport weight is pretty thin even with 129 stitches. How long is your cable? What I'm asking for is if it's too long you'll never be able to make a single loop circle circle (like with a 16") without stretching it unless you've got a cable long enough for magic loop.
I make hats for charity and I use the magic loop method. For hats I always use a 40". You can do a modified magic loop, but I don't care for that method myself. If you have two needles you can use two with needles the same size.