If turning a rod half a turn, won't I then have to re-sub-trim, thereby throwing off ATV's for that channel??

That's what YNOT is getting at. Sometimes a slight error in the other direction counters your initial problem.

I know you are an experienced pattern pilot and you know how to set up linkages. When I set up my 3M Extra using 4 elevator servos, I had 14 servos to choose from, luckily out of that, I found 2 lots of 4 that matched perfectly. I used the other 4 on the rudder tray. If you have some more 8611,s it is worth swapping them around until you find the best match between them.

On the odd occasion where I have been unable to get them dead right, I have set it up so they are perfect on the sequence flying rate as this is the most important. then the snap and 3D rates have been slightly off.

Hope this helps
Alan