I know it's not as easy to do, but adding span is much more effective than adding chord. Increases in chord are likely to only marginally increase pitch authority, or possibly even decrease it (if the servos stall as a result), while greatly increasing the load on the servos.

Diane Hakala (US acro team) showed me her early Staudacher in 1996 at a full-scale acro contest in Chandler, AZ and explained that she was having the chord on her elevators reduced by 3" to lighten the stick-force-per-gee, without decreasing their effectiveness noticeably. So, if you have two elevators with the same area, but one has a large chord/small span and the other has a longer span/short chord, the longer span elevator will be more effective and require less force to deflect.

If you have an abundance of available servo torque, increasing chord might work for you. It's jut more efficient in terms of servo and battery life to do it the other way.

Control surfaces on racing airplanes are generally made as small as is safe in order to reduce drag. I know your objective isn't overall minimum drag but this illustrates the point that deflecting large control surfaces requires a lot of energy.

I'd use something lighter than lexan, like balsa per BMatthews. Or I'd build new elevators with large counter-balances.