I was having trouble with thermal expansion/contraction which caused the rudder and elevator trim to be inconsistent on my 4*60. So I bought some carbon fiber control rods to replace the nylon rod type ones that came with the ARF.
The CF rods are very lightweight and have very low friction as they slide inside the outer tubes. The problem I had is that they are extremely flexible. So, if you choose CF rods for retrofit, be sure they are supported as close to their terminal ends as possible with the outer tube. If you don't, they will flex too much when you move a control surface when the servo arm pushes them (push-pull system).

Since I was experimenting, I ended up trying two different methods to replace the original nylon rods that came with the ARF. Both methods entailed using metal rod material. I cut 1/4" pieces of nylon rod from the original control rod and CA'd them every three inches along the metal rod. The nylon rod pieces work as bearings. This method worked fine, but you have to make sure the two end bearing pieces are long enough so they don't come completely out of the outer tube at maximum travel.

I used the Great Planes control rod for the second method. It's the same idea as the method above, but you cut "bearings" out of their low-friction material and glue them onto the rod in a similar fashion. Seems like the price of the Great Planes control rod was reasonable.