It's been my experience when bare-shaft matching folks with arrows, that shorter bows tend to need higher spine than longer bows of the same draw weight. This doesn't necessarily mean they're faster, though. The abruptness with which the force is applied is greater with shorter working limbs, which explains why higher spine is needed to compensate, but total energy output might be the same or even less, depending on multiple design factors. Speed and spine don't necessarily correlate.