i work with a turboxs mechanic and he builds trans for the wrx since they are the weak point in those cars also. some people went to the sti 6 speeds and it slowed there cars down (wieght and gear ratios) so ppg built the 5 speed gears sets for the car and they are flawless lighter not breaking yada yada.
aslo it doesnt have to be just a dog box they make 1-2 straight cut sync or 1-2 dog with 3-4 straight sync, they make a much stronger helic cut sync gear set that nobody has broken yet so there are more options than just a strickly straight dog box i will putting one in my car probably a 1-2 dog and 3-4 sync straight. which many of the wrx's have as daily drivers