I never take anyone's word for anything, but I do listen to advice on what steps I might take to find out my own truth. So I will be trying DPP out and directly comparing it as best I can with LR's demosaicing. Given the high quality of 5D MK II images, I can stand a small hit on quality of finished image if DPP doesn't quite cut it, simply because LR is almost unusable now for me so a small hit on quality is far better than not getting any work done. I'll try doing an image tomorrow and see how far I get with it.
I do appreciate all the ideas and advice though, even if I do forget the odd nugget! 