Ok, I am late to the party again. All this talk of "Ackerman" is really confusing and then I remembered what it was all about. IF you do pull-pull, there are two different ways it is commonly done.
One way is from the outer hole in the servo arm to a pull station on the control surface. This is where the "Ackerman" issue generally makes itself noticed. What it means is that the control surface pull station mounts need to be the exact same distance apart as the powered (from the servo) end. Otherwise the geometry will allow a slack cable when NOT at neutral.
The other way is to use a tiller bar (several different vendors sell them - Dubro, Sig, and others) and make the pull station on the control surface exactly as wide as the attach point to the tiller bar to avoid "Ackerman" problems. The tiller bar gets its 'power' from the servo.
As for CG issues, pull-pull CAN help a lot if you are careful. Right now I am working on a Gere Sport. I have flown another version of this bird before and all versions I have seen needed between 5 and 10 pounds of lead in the nose to correct the CG problem. So on this build I have moved from servos behind the cockpit with long carbon/glass rods to the control surfaces (where someone else had already installed them) to servos in front of the GG with short carbon/glass rods to just behind the cockpit where I have installed tiller bars. The difference in CG correctional added weight should be substantial. The control rods and (1/4 scale) servos weight over a pound and much of that weight is being moved over 12 inches FOWARD. I estimate the CG corrective weight change to be in the neighborhood of 3 pounds. We shall see...
The reason I spoke of this is that the tiller bar takes all the pull-pull load and does not transfer any of it to the servo. That means I am going to (probably tomorrow unless the carb rebuild I am doing right now goes well) make those lines as tight as I can get them while holding the tiller bar at neutral. As someone else pointed out that should help avoid flutter (can you imagine flutter on this beast?).