Rpm vs mph???

[superek4]

I hv this 2 motors n want to know what's the diff between these 2 set up?

I am using 6s lipo n on a CRT.

1.neu-1515/3d with 16/50spur speed 37mph, 30192 rpm

2.medusa 1600kv with 13/50spur speed 35.41mph, 35520 rpm

i am confused do we measure by speed or rpm? so which setup is faster? less rpm means less torque?