If two runners have identical stride rates, the one with the longer stride will win.
If two runners have identical stride lengths, the one with the faster stride rate will win.
There's a happy middle ground in there somewhere- I just don't know where.
New runners have a tendency to stride long, but very slowly (overstriding slowly). So, it can be very beneficial to teach them to increase their cadence in order to improve their overall speed. Once you have them striding at 165-180 strides per minute, then begin focusing on their stride length and tinker with that a little. Chances are that once they get the cadence down, their stride length will sort itself out.