WEll...
First of all, i think plasma mode was intended just for plasma cutters. So i believe that setting should be off.
If you want precision you should stick to exact stop since there is no way to remove the corner rounding completely, even with high acceleration.
But as you say, exact stop is too slow, even with high accelerations. Specially, ive heard ARTCAM outputs many tiny little segments in their posts, you could try increasing the lookahead lines, although i think you will still see little increase in performance.
Your machine looks rigid, but only you can be the judge of your machine handling such jerks.
Fernando