Typically, those who use expo, use it to reduce the travel that they actually use for flying. That has the same disadvantages as using ATV/EPA. If you change the linkage instead, you will increase the mechanical advantage.

Dual rates have the same problem. If you never use high rates, change the linkages to match your low rates. You will increase the power available at the control surface by 30 to 50%.

On the other hand, if your type of flying uses high travel rates, even occasionally, you will not be able to set up these high mechanical advantage linkages and you will need to go to high powered servos. The best a 3D flyer can usually do is 1 : 1, which is no mechanical advantage at all. A 120 oz servo set up at 1:1 (for 45 degrees of control surface travel), gives less power at the control surface than a 42 oz servo set up at 3 : 1 (and 15 degrees of control surface travel).

Most sport planes will easily do any non-3D aerobatics with 15 degrees of elevator travel. Although, as Bubbagates said above, you may need to go to a higher powered rudder servo if you do much knive-edge flying.

I didn't mention 6 volts. That is also a good way to increase your servo power. In fact, most standard servos are rated at more than 54 oz. when running on 6 volts. Just remember that the servos will draw more power at 6 volts, so you will need a larger onboard battery.

Jim