McCaffrey's Pro Day stats compared to the 2016 Combine:
40: 4.46 (7th at Combine) *4.36 unofficial 40 time
Vert: 36.5" (8th at Combine)
Broad: 122" (19th at Combine)
Shuttle: 4.15 (9th at Combine)
3Cone: 7.09 (19th at Combine)
Jeff Janis's 2014 Combine Stats and ranking:
40: 4.42 (8th)
Vert: 37.5" (13th)
Broad: 123" (8th)
Shuttle: 3.98 (6th)
3Cone: 6.64 (3rd)
You did say football speed, but in terms of pre-draft measurables there is a negligible difference between the two athltically. Returners are more valuable than gunners, so if McCaffrey shows anything as a returner combined with his contributions at WR I think he could get the edge. Janis had a nice game last week, I hope he's turned a corner as a WR.