For this type of plane, coreless and metal gear servos is overkill. Have a look at Hitec HS-85. They are just as strong as a "standard" servo. The Futaba "equivalent" according to thier web page is the S3102.
http://www.futaba-rc.com/servos/servo-compare.html
In my book, price wins for this one.
Are you doing the optional flaps?