In this paper, we theoretically investigate how the momentum width of an atomic source affects the efficiency of Bragg beam splitters and mirrors. We conclude that narrow momentum width sources, such as atom lasers, are significantly more efficient than atomic clouds with a larger momentum width, such as thermal sources, for high (but accessible) order Bragg processes. The development of large momentum transfer (LMT) mirrors and beam splitters is one of the most promising paths leading to increased precision in future sensors based on atom interferometry. This makes these results significant, because the signal to noise ratio of an interferometric measurement scales linearly with the momentum imparted in the beam splitting processes and scales as the square root of the atomic flux.