Okay, I think i have a handle on the problem. Firstly the red 'staining' I'm seeing on the black suits is both noise and also moire (the 10D wasn't resolving enough individual thread detail to produce this much moire!) which is why it it sometimes painfully apparent even at iso 100. It also explains why sheer black material, such as in a dress is much less affected while suits, especially with pin stripes, or with a two tone pattern suffer horribly.
ACR smooths both the moire and the noise with it's 'color noise reduction' tool so that instead on red dots (noise) and red swirls and lines (moire), I'm getting a red staining over parts of the black, specifically the darker areas.
Once ACR has established this stain then even darkening the blacks, either with the shadows or contrast slider, does not eliminate the red, but just darkens it.
I'm in the middle of playing with a couple of sample images, to see whether noise programs can remove instead of smudging the colour noise, so that I can leave the 'color noise reduction' off in ACR and apply a noise plug-in as part of the workflow in an action.
Other than that, I've noticed that DPP accentuates the problem less in the first place, If they had an ACR like interface so batching hundreds of RAW files at a time wasn't such a daunting prospect then I would use it.
I remember Michael in his original preview of the 1Ds noting the moire and mentioning that it would drive fashion photographers mad (I least I think that's what he wrote), I guess this is the same thing.
If anyone has any suggestions or has come across this problem then please let me know.