eeipshy,
I would go with a standard size servo on this plane, the hs-55's are just a bit weak as those are used for park flyers most of the time, if your looking for cheap go with these,
http://www2.towerhobbies.com/cgi-bin...?&I=LXN586&P=0

If it were me I would go with these if I was using Hitec, you can never have to much servo.
http://www2.towerhobbies.com/cgi-bin...?&I=LXUZ87&P=0

These would also be good choices, if your a Futaba person,
http://www2.towerhobbies.com/cgi-bin...?&I=LXH296&P=0
http://www2.towerhobbies.com/cgi-bin...?&I=LXFKZ8&P=0

Don't worry about putting stress on the wing, it's the servo that has to deal with the stress.
Most all servos will fit in the wing.
This plane can handle the extra weight.
That wing will rip the gears out of that 55.

I looked at this plane on the web site, and it could be possible to go with HS-81 w/metal gears if your intent on sticking with mini servos. the plane is smaller than I thought. I would probably be in the 30-50 oz in of torque for that plane, sorry I don't do metric.