Nigel, please let us know what you come up with with your comparison results. I did a comparison myself a few weeks ago(R2880). Not scientifically, just eyeballed it.
I printed on Canson Photo Satin. I converted an image to B&W in CS5. Once happy with it I used this image for my at home comparison. I never tried using ABW as a converter since I want to know what my image will look like long before it goes to the printer.My understanding from a tutorial is that you can send monochrome RGB, Colour RGB or grey scale RGB to the advanced black and white mode.
I still have my comparison prints from a few weeks ago. Of several images, I found it was difficult to tell the difference between using photoshop manages all the colours or letting ABW manage all the colours. I didnt make any changes or toning in ABW. Just printed it the way it is by default. Except for one thing...I set the tone to 'dark' or sometimes even 'neutral' or 'normal' instead of the default 'darker' because this makes an observable difference.
in my comparisons i tried all combinations to see what would happen. I tried PS manges colours and then turned ABW on too to see if ABW would take over, which it did. I tried photoshop manages colours ONLY and turned ABW OFF. I then also compared letting ABW only manage the colours. I have to say, in my comparison of one paper, that thw ABW print was very neutral,and had a very nice grey, whereas the photoshop manages colours print had a kind of cast to it. I wouldnt be able to tell if I wasn't holding both images up side by side . but the image where photoshop manages colours had a kind of different colour to it. i guess it was a cast. it had a slight , very , very slight purplish tint to it. very hard t tell if you were not holding the images up side by side. Probably wouldnt notice it unless you're an expert.
so i prefer to use the ABW mode whenever doing my B&W prints so far. Of course, when I am doing duotone or quadotone images, I HAVE to let photoshop manage the colours and turn the printer control OFF>
Just wondering, if I have already created a black and white image I am happy with in ACR/Photoshop, is it still advantageous to print in ABW mode (using an Epson 3800)? )I have an idea that the benefit of ABW is more about neutrality rather than a B&W conversion tool) If the answer is yes, would this still be true if I wasn't using a paper for which an ABW profile is available, or would I be better off then letting Photoshop manage colours using the correct printer/paper profile. Of course I can and will test this for myself, just wondered if there is an "official" view?
PS Just upgraded my Photoshop by 3 versions so playing with lots of new new toys in ACR!