For Comping mode, any previous Takes are muted. However, there still seems to be something processed in I/O for those muted takes. If arming 20 tracks, for example, on the second or third take, I experience Audio Dropouts. This happens even though Sonar mutes those earlier takes.
 
Is there a way to free Sonar from dealing with previous takes (other than muting them) until after I stop the transport?

Since you might unmute something at any time, SONAR has to be buffering all takes in all active (non-archived) tracks all the time. But if you're getting dropouts as takes build up, it's probably the disk bandwidth rather than CPU load, and you can probably overcome the problem by increasing disk I/O buffers.

Increasing I/O buffers had no effect. We tried many iterations of that in test. The only workable solution for us was to delete previous takes, saving each take as a new project, then manually clear out any excess Take Lanes created.