I would say the Chisos would be warm to low-mid 30s if it's anything like their other bags. As far as it getting you down to the mid 20s, that would depend entirely on the rest of your system, but it looks like it'll work for you. Though in stretching the temps that much, you might be better off getting the palisades and carrying less clothing, as that would get you to the right temp with just base layers at most, and only add 3 oz.
Other than that, if you want something with a full footbox and a draft collar or the equivalent, I don't think you can find anything that matches katabatic in their price range. Nunatak makes great products, but if you don't need custom, I would stick with katabatic.