"I need this saw to atleast be able to turn a 24" easy. My husky 55 i think is going to get a 20" i want something a little bigger when i fell some bigger oaks."
It takes closer to 75-80cc to effectively manage a 24" bar, IMHO. Sure, smaller saws will run them, but they are not efficient with them in big wood.
I have a 262XP, and a 268XP, both are strong runners, and much faster than an Echo CS-670. I don't feel either is well suited to a 24" bar. I use a 20" on the 268XP, and 18" on the 262XP, which they manage easily.
I've owned two new CS-670's, and have a rebuilt CS-6700, they are "weak" compared to the Husqvarna XP's, and pretty much maxxed out with a 20" bar on them.
No experience with the 600, but I would doubt it's well suited to bars much beyond 20", and probably ideal with an 18" 3/8" full chisel set-up......FWIW.....Cliff