There probably isn't that much of a difference in feel on the two. The 67.8 will be a little easier on your knees, a little more aerobic, and a little slower at the same pedaling cadence. The 71.5 will be a little harder on your knees, a little less aerobic, and a little faster at the same pedaling cadence.

If you are going to be using brakes to stop, I'd recommend the 71.5. If you are primarily going to be using the drivetrain to stop, I'd go with the 67.8.