Walcott relies on pace, yes, but also the timing of his runs, the intelligence of his runs, his first touch, and his finishing. However, his pace is phenomenal. When he naturally slows down a bit, he is still going to be really, really fast compared to everyone else for another couple of years. Contrast that with Giroud; when he goes into physical decline and loses even a fraction of the 'pace' he has today, then what will he have?