I've been riding a Gunnar for about a month now. I like the frame, it feels great. I don't anything about the Kelly, but I can guarantee that if you buy the right size frame of the Crosshairs and part it well, you'll love the bike. It's not the lightest of frames, but it shouldn't be. They should be slightly overbuilt for off road.
The guy I bought it from was a roadie who worked the lbs. He thought it was a bit too small for him, and gave me a deal. So I would suggest that you find out which frame size is right. The Gunnar has a somewhat longer top tube than some cross bikes, such as a Surly, and you may want to choose depending on what top tube length you need. The seat can always be adjusted much easier than a stem.