We had a jib that was similar to the J cut. We tried it out in one design racing on the SF Bay our first year. What we found was that we had too much sail up high. In our wind conditions (20+knts) a lower cut sail would always out perform a high clew sail. You could sail faster and higher with what was termed a “deck sweeper”. I believe the reason was a high clew sail would cause the boat to heel more. Under the right conditions I think the higher cut sail would do well (more wind up high).

If you try it out I would be interested to hear what you think.