>>719968946
There are only two disguises that don't slow down a Spy, Medic (base speed 107%, same as Spy) and Scout (base speed 133%), and out of the two Medic is probably the riskier disguise. A Medic is expected to be near the frontline constantly, to heal everyone and to build up and maintain overheal, an idle medic just sitting behind a Heavy or skulking around an Engie's nest is far more suspicious than a Scout that's siting outside the Enemy spawn. Scout's expected to be everywhere, mainly near the enemy causing trouble and being a general nuisance, but sometimes they can be found in their own base hunting a Spy they saw or another scout that's trying to rush intel in hopes they don't have an Engi nest near. This lack of general expectation makes it perfect as a disguise since no matter what you do it's something that a regular Scout would be doing too.