Don't strain yourself trying to increase your hand span beyond that which is musically comfortable for your hand size. Many stride and swing players cannot stretch all tenths, especially with other notes included in the middle. And many who can stretch them do not play them straight all the time anyway, preferring to use a large number of broken tenths, either upward or downward, for their rhythmic effect and variety. Even Waller, who had an enormous hand, did this to superior effect in many of his solos rather than just bang them down all the time. For myself, I think straight tenths sound nicer in slow stuff, blues and the like, than in fast pieces. This is because the faster you play, the less discernible, and therefore less important, left hand harmony becomes.
I think we have all struggled and strained trying to do some particular movement which is very unsuited, or even impossible for our hands. Common sense usually sets in when we realise that the musical effect is not worth the bother. It is easy to allow some specific aspect of technique to become a neurosis out of proportion to its musical result - bad for the body and bad for music.