Morning J_T,
Recent thinking appears to be that the decision is made before V1 in that, if you have not already commenced stopping, then you are committed to going.
Doesnt that make it an action speed? If you have started to do something by V1 then you are committed to going?
Idunno, older aircraft were certified with the engine failure at V1 and a specific response time during which time that aircrafts speeds was constant, this has now changed to having the engine failure 1 sec prior to V1 (Vef), so that the decision to stop is made by V1, the aircraft also accelerates during the time that it takes to transition to a stopping configuration.
Mutt.