Great Ken! Next step is to totally focus on the sights and the trigger so that you hit the X with confidence. The quick six are the final six shots and I often feel a bit nervous, especially when the previous 144 shots have been good. Knowing that you easily shoot X almost regardless where you aim as long as you see the top of the target helps a lot. This of course works for match 4 too. Use the same technique and make sure to use all the time.
I used to do a lot of ISSF rapid fire pistol some years ago (shoot 5 shots strings on five targets in 4 to 8 seconds with a .22 short) and I reuse the training methods my coach taught me.
One really useful practice is to try too shoot the last shot exactly when the targets turns. Then that becomes easy you add disturbances; shoot first shot really late - then adapt and shoot the rest of the shots at an even interval with the last exactly when the target turns. Similarly; shoot first shot really quick - adapt, use all the extra time you got from that and shoot last shot when the target turns. If you do not have turning targets an mp3-player with commands and timing for 12s/35s matches works great too.