Thanks for all answers !
To summaries it the 2x2 have the following advantages over the 90-120 size :

1) ability to adjust the wing and the stabilizer incidence
2) Better servo's are usually used
3) Better Power ratio

now all the above are accessories and i guess you can have them all on on 90 size airplane ..

what i am more interesting is whether the 2x2 airplanes have better aerodynamic characters that makes them fly better

good example will be Focus sport vs Focus 2x2