Hey Bluebearee. One difference is weight. The Vapor Ki weighs in at 2 lb 2 oz. The Lattitude Ki is 3 lbs 14 oz.
I used a Nimbus Ozone with women’s hipbelt on my PCT hike and it was great. My only problem resulted from the fact that the outfitter I bought it from convinced me to buy the wrong size. (I should have listened to the alarm bells ringing when Jeff and I weren’t put in the same size packs, as we have the same torso lengths.) Other than that issue, the pack was very comfortable, the women’s hip belt fit well on my hips, and I love its simplicity of design.
I’ve been checking out the rest of the Granite Gear line since my last hike. I looked at the Nimbus Lattitude Ki when it first came out, and my only thought was “How can they have made such a simple pack into such a complicated heavy beast?” The Nimbus Ozone, Vapor Trail, and Vapor Ki are simple top-loaders with only a couple pockets on the sides. The Nimbus Lattitude Ki, though, had all kinds of zippers, was front-loading, had an added “hidden” lid, and other stuff that just seemd like clunky extraneous weight. I just wasn’t impressed.
The Vapor Ki is just a women’s version of the good old Vapor Trail, my husband’s beloved pack, although they somehow added 2 oz to the women’s version in the conversion. The Nimbus Ozone is basically VT, but with a sturdier suspension, interchangeable components, and more back padding. The Ozone weighs in at 3 lbs.
Personally, I’d check into the Vapor Trail (since many women use it and like it), The Vapor Ki, or the Nimbus Ozone with women’s components.
Chipper