For Co2 you might want to look at the Airforce condor/talon. Any length barrel you want. Any size Co2 bottle you can find, yea. .177, .22, .25, or any custom caliber barrel you want, or one of each if you like. http://www.airforceairguns.com/category-s/103.htm Airforce air rifles are made in the U.S.A.
I'd go with the QB78. I may be mistaken, but I think that the XS60C is pretty much the same as the Umarex Fusion. If it is, the O ring seal on the end cap of the CO2 tube has some real problems. http://hardairmagazine.com/reviews/airgun-test-reviews/ham-test-review-umarex-fusion-air-rifle-177-cal/Any input from owners?
I don't think you can beat a Crosman Discovery for what you want. You can find refirbs and used for under $200. Dual fuel so if you ever want to go HPA or pump you can. Easy to fill from a paint ball set up. Tons of mods available. Wood stock and it just begs for things to improve it. It looks good too! IMHOJudd