Thanks guys, your thoughts were interesting and informative. I decided on the 22 mag for the following reasons. Heck, who am I trying to kid. For what I'm doing there is no strong justification in choosing one over the other or even choosing a new rifle. If I was being totally practical I would probably have bought a 22LR for the 100 yd shooting I specified. However for what target grade 22 ammo costs I can buy ammo for any of the other three calibers mentioned.

As for rimfire over center fire. I ether still own or have owned and reloaded for 22 Hornet. 222. 223 and 22-250. So I'm at least familiar with the older 22 center fires. However most of my varmint hunting was actually either done with a 22 mag,32 S&W Long, 32-20 or 7x57 Ackley Improved. Sometimes though I just want to take an accurate firearm to the 100 yd range or back pasture without thinking about reloading or retrieving brass.