Pedrith, although you like the look of TA, it's wise to remember it's only real benefit is in realism and accuracy.

Personally, if that scene of yours were mine; I'd freak-out at the thought of doing it with TA (it's just 'too' slow for that kind of scene).

If I were you, to light that scene; I'd switch-off TA and even the Sun/Moon. Instead, I'd use just one VERY strong but VERY distant radial, carefully tweak the Volumetric settings for it, and use Volumetric-World. Then just tweak the ambience level of your materials to give the impression of ambient light. It would still take a while to render, but nothing like using TA. Len.

The wait can be horrific, but the outcome can be worse - pumeco 2006