The most important thing in an OWB holster for a 3 inch 1911 is that the holster and belt are stiff enough that the gun's grip will not tend to swing away from the body. If the holster sits high on the belt there isn't much gun barrel and holster below the belt to stabilize the rig by pressing against your hip, and the force of gravity can make the gun's grip and the holster pivot away from your body, causing printing on your cover garment. So it is important to pick a sturdy, stiff holster that doesn't sit too high vs. the belt.
A horsehide holster in this application has the advantage of stiffness compared to most cowhide, or a cowhide holster made of thicker leather will also work. I have a 3 inch Colt Defender, similar to your Kimber Ultra, and have tried several holsters for it. A good choice is the Kirkpatrick Compact Under Cover, which is pretty sturdy and stays put. It is also available fairly fast - I got mine in a week or 10 days, and it cost $54.
Kirkpatrick Leather website