Hi @aguy - Thanks for reaching out!
You are spot on that the Co-op Trailbreak 30 and Kelty Cosmic Synthetic 40 bags are similar in many ways. With the Cosmic's wider hip girth, that bag also has a larger volume. This may be what you're looking for if room to move around within your bag is important to you. If you are planning on going backpacking with your new bag, the Trailbreak 30 will take up a bit less room in your pack, allowing you to bring along more of other supplies.
Let us know if you have any additional questions and we'll be happy to help!