I currently have 208 st of City Tweed HW on a 24" circ!
I love to work with them all jammed together. It's easier to "queue" the stitches on the lefthand needle! Not as much tugging and pulling them up to the tip!
When I first cast on the 292 st, I used a 32". But as I worked the decreases up to the waist...I dialed down my cable length.
Oy vey! For 576 stitches on your blanket??? At least a 40"!
It will be nice and crammed!