I used to race on full sized IOD class boats which are basically a scaled down J boat:
Like the J (full size and model) the classic 6, 8 and 12 meters (and the EC12), these boats have long overhangs, narrow beam, long heavy keels with an integrated rudder. The boats are sailed with a lot of heel.
Anyway, the skipper of the boat I crewed on was 9 time world chapion of that class and was considered to be one of the fastest sailors. If the race came down to a boatspeed drag race, he would most likely win. He had a feel for the boat that allowed him to sail very fast.
I sailed with him for about 5 years and learned a lot about what it takes to sail that classic style of boat. The most important thing I learned is that if you have any helm at all, the boat is slow!
It was not uncommon for my skipper to announce “I am getting some windward helm, lets make a change to the sail trim.” He would then work through a list of changes. He had a specific set of measurements of sail shape that he used. For example, when laying on the floor of the cockpit, if you extend your arm and sight past your fingers to the gap between the leach and the backstay, you could measure the twist of the sail in terms of finger widths. so the first question he would ask is “what is my leach?” to which the mainsail trimmer would reply “you have a 3 finger main.” My skipper would then make a change to that depending on the conditions. He might ask for a 4 finger main or he might decide that the traveller needed to be dropped down. You get the idea. Then, as is the case with heavy boats, he would wait. 10 to 15 seconds would go by before the boat would have fully adjusted to the change. Then he would re-evaluate the situation. Did the helm get better or worse? We would use paralax to judge our boatspeed relative to other boats. Were we moving faster or slower? Pointing higher? Etc.
The bottom line is that on these types of boats, you do not want any helm at all. You should be able to drive a classic 12 Meter with your finger tips on the tiller.
If you need a massive servo to keep that boat sailing straight, then more than likely you are not sailing fast. It is not a matter of having a balanced rudder. The rudders on these classic designs are really little more than a tab off the back of the keel. If your boat is balanced, then that tab of the back of the keel will be balanced. You should not need such a big servo to drive that boat…