balance was a major concern of mine but see for yourself how she sits. Ill try to dig up a pic w/o jp for a comparison. When i initially bought the boat it had the crank in the starboard rear compartment, and the 2 TM batts in the console. As we all know, w a full live well and don't even get me started on a full release well! you are gonna need to use tabs, no way around it. I wanted to add a house batt anyhow so decided to move the TMs to the front, crank along w a group 27 house batt to the console. This did help with weight distribution.
In the end temptation and the great price i found on a CMC JP got the best of me. My theory was that added weight effect of having the engine further back was balanced by the movement of all the batts forward. Yes, moving the batts forward did hurt the top end a little but that was almost gained back by the jp. fastest combo would be batts in back plus jp but that wouldn't be practical.
The setback of the CMC is 5.5 inches plus the setback of pp bracket (.25-.5?) so close to, if not 6 inches total. Agree that 4 inches wouldn't be with it nor would i go to 8 inches as i believe the 6inch keeps the boat in harmony.
Can't comment on stress to transom as I'm not an engineer but since my neighbor and good friend now owns the boat i can tell you he hasn't had any issues with it. All kidding aside, i can't see why it would hurt it unless user error.
Speed gained top end should be about 1-1.5mph, and avg increase of 100 rpm and that was with the 20 pitch ultima. saw 56.5 with minimal speed runs and 5.4krpm. My buddy switched back to the 2+2OT which has a smaller dia and 22 pitch. Im curious to see what we can get out of her now. my guess is 5.3-5.4krpm and over 57.