Why 22-250?
I recently sold my .223s and converted to .204 Ruger. I have used the .204 in the field and on paper out to 500 yards. It flat out performs.
Here is a good read on the .20s.
http://www.6mmbr.com/20Caliber.html
Excerpt:
The Velocity Edge--A .204 Ruger drives a 40-grainer 600 fps faster than a .223 Rem can push the typical 22-Caliber 50gr bullet. This higher velocity produces a flatter trajectory. Additionally, grain for grain, 20-Caliber bullets have higher ballistic coefficients than .224 bullets. Combine this with the extra velocity of the 20-Caliber, and you get superior performance in the wind. Run the numbers and you'll see--a 40-grainer shot from a .204 Ruger has less drop AND less wind drift than a 40gr or 50gr bullet fired from a .223 Rem. You'll find the data in the chart below.
Component Economy and Barrel Life--All the Twenties burn way less powder than a 22-250, and the smaller Twenties use less powder than a .223 Rem. This attribute actually has two advantages. First, it makes shooting 20-Caliber cartridges more economical, but mostly it means less barrel heat. A typical varmint hunter may shoot several hundred rounds in one day, so barrel heat is an important issue.
Terminal Ballistics--For hunters seeking maximum explosive effect on a small varmint, Twenties deliver the goods. Because it passes through the rifling much more quickly, a 20-Caliber bullet will be turning much higher RPMs than a 22-caliber bullet launched from a barrel of similar twist rate. Experienced varminters will tell you that high spin rates create the most explosive impacts. On the other hand, if you shoot a non-fragmenting bullet, the Twenty can minimize hide/fur damage. If you plan to keep the fur, you want the smallest possible hole or damage to it.
Another good .204 read authored by a friend, hunting partner and fellow member of THR....Dr. Ken Lunde.
http://www.6mmbr.com/gunweek047.html
I have had good luck with the Tikka T3 Varmints. While not as pretty as a Kimber (or my Coopers)......Tikka makes a good barrel. They are truly sub 1/2 MOA shooters.