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As a result is I get artifacts and jumpiness when the movie is produced.

The reason you get artifacts is that the AVCHD render engine is substandard in PD7. Any rendering will cause the artifacts. I use native video at less than 14800kbps and get crystal clear images from the camera. As soon as it is rendered at the same bitrate it intoduces artifacts.
The only way to avoid it is to use SVRT and of course you are stuck here as well because as you say, the bitrate limit is exceeded.

I am hoping the rumours about a new AVCHD render engine will come to fruition.

The best way to preserve image quality is to render to Mpeg2 BD profile but of course this doesn't help you if you want to use hybrid DVDs.