The first question that I have is are you talking about the speed in which the airplane rolls? That really and as speed decays on an upline and you start loosing some aileron authority is about the only thing that the aileron cord is going to affect. To obtain really good axial rolls requires that the airplane be set up correctly at multiple points. It will require some measuring, changing of the wing incidence and most likely a CG change. It will also require a number of test flights. I of course would be more then happy to get into greater detail if you want. I only ask that if I take the time to do so that you are ready to give these things a try.

Ok, let's adress the ailerons first. Have you measured the throws to make sure the travel is exactly the same for both ailerons up and down? I'm going to assume no. Most guys don't. The first step will be to measure them and adjust them so both ailerons have the exact same travel going upward. Then adjust them so that they have the same travel downward except you want 3/32" less downward movement then upward. This is referred to as aileron differential. It is needed because the aileron deflecting down generates more lift and drag then the upward aileron looses lift and produces drag. The result is when aileron is applied the airplane wants to yaw opposite of the roll direction and pitch up slightly. Second step is to add 1/16" positive wing incidence. The symmetrical airfoil must have some positive AOA in order to generate lift. With a zero zero setting you must add some up trim and you are flying the entire airplane at a positive AOA. That little bit of up trim screws up anything that is not upright level flight. Adding the positive wing incidence will require the CG be moved just a tad forward. Maybe 3/16". The next change would be to add right thrust to the engine if it is not already there. A total of 2 degrees should be fine. This is done to offset the engine torque that wants to constantly pull the airplane to the left.

3/16 is a bit much on differential. It could be part of your problem. Please keep in mind that these are a set of parameters, doing just one will not result in much of a change.

Good call on sealing the hinge line. For an airplane of that wing area and relitivly small ailerons the 3/32" differential is going to be pretty darned close. You are correct that in order to get it spot on is going to require some flight tests, I mentioned that in my first post.

More roll authority is one thing and roll precision is something else.

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A well set up Stik will hold its own. In his very early days Chip Hyde flew Pattern with a Stik. As far a roll authority goes, even the smallish ailerons should give you some pretty rapid roll rate unless the aileron servo(s) are not up to the task. You may want to share some farther details about your setup.

Looks like you could safely with some aluminum servo arm increase the servo arm to 1” and get more throw. That is provided you have throw maxed out in the TX. Also if you have dialed in s bunch of expo it will seem to slow rate down a bit. .18 servo speed is a bit on the sluggish side as well.

More like .75 degrees. The test for this is to trim the airplane to fly level at full throttle and pull to an upline. If the airplane pulls towards its back it will need more positive. If it tucks towards the gear, it has too much. Once the wing incidence, CG , engine thrust and elevator trim are in sync the airplane will do a straight upline and will fly at either 1/2 throttle or full throttle with zero trim change.

Here in California we have had rain every weekend for what seems like months. I haven't flown since December 30. I'm sure some of these trimming techniques will improve the performance of your airplane. They are derived from what I have learned by competing in IMAC and pattern. Going through the complete process of trimming a model is a rather long process that requires many test flights and small adjustments but well worth the efforts when done.

Not really, I went a couple decades of flying before I really started paying attention to a proper setup and trimming. As long as you are having fun and the airplane meets your expectations then it's all good. When ready you started asking questions so I say " good on you "!