Pardon the delays, Fligh. Seem to have turned up my error:
My normal map featured subtle aliasing errors on certain UV edges and this, coupled with exaggerated settings on my texture panel, resulted in horrid ‘tears’ at render time.
Overall, I learnt two things:
i) To successfully render detailed displacement maps, you seem to need an INSANE polycount. Subsurf (render only) seems to accomodate this.
ii) Normal & displacement settings on the texture settings slider seemed to be remarkably sensitive in some cases. Don’t be alarmed if you’re setting you normal slider to 0.025 to return a successful render.
iii) It really, really pays to check any normal maps, displacement maps etc in photoshop (or gymp) prior to importing them into blender. Watch for aliased edges at the perimeter of your UV map… it just takes a touch of aliased white to ruin your render.