nikolas,
what i am saying is that Extreme Flight strongly reccomends metal geared servos. If you were to put a 1.40 on a 60 size airframe when they only reccomend a 60-90, and you say your wing broke off and you thought you heard flutter, they would say "maybe because your engine was much larger than the reccomended size?" same with the servos. chris is a very personable guy and it very pleasent and fair, but if you have a failure and it is possible that it is servo related and you did not follow his reccomendations, he will most likely not stand behind the product, and rightfully so. If you bought a computer with a warranty and you overclocked the processor, do you think warranty will cover it?
however, the servos will probably physically work for the yak.