agreed...with a Saito 100... standard servos are enough... but anything more and you are going to get flutter and definite blowback...

example...

I had a .60 size plane that just would not KE....... I upgraded the rudder servo to a 5645.....and now the plane will HAKE the length of the field...
I thought it was the plane, but it was the servo not able to hold the forces....
not "hard" data... just my real world experience