The above said, I did play some more with build 1.0.0.27 last night and I'm definitely seeing noticeable performance improvements.

Also, once I reconstructed the scene, which had developed crashing or corruption of some sort, when using the 1.0.0.13 DSON Importer build, I have managed to open the reconstructed version of that scene, using the 1.0.0.27 build.

So much better, although it definitely still needs further... I think quite radical... optimisation, in my opinion... and to fit my needs, at least.