For sure short speed might go like S2L and speed endurance more like L2S. I don’t think that there is just two ways to progress towards speed endurance like doing 2x300 (L2S) or split runs like 2x2x150 (S2L) making overall volume exactly 600m. I think there would be some place for intensive tempo during the end of GPP and the begining of SPP b/c you get speed from doing short speed sessions. Speed endurance sessions above 95% intensity would be run anyway during the last stage of preparation. I know Charlie didn’t advocate speeds below 95% or above 75%-80% but I think that there might be some place for intensive tempo. We know that there is no one way to Rome.