Thank you to all who have kindly taken the time to reply, often in such detail. I am extremely grateful.
It would appear that there is no clear-cut answer. As is so often the case in recherché issues such as this.
A number of possibilities present themselves:
1) that consumer flatbeds have recently come up to scratch but that some very experienced users have not been able to test everything all the time and are therefore a picosecond behind the times
2) that those who believe the consumer flatbeds are up to the task I set them are in some way less fussy or discerning than those that disagree with them
3) that there are so many angels on the pinhead that it's very hard to count them accurately
I will purchase (and I suppose more or less at random!) a 750 or M1/F1 and use it for proofing scans - but of course I'll also try to print to my target size from the files, having played around with various ways of slicing and dicing post processing. And then I'll know what the truth is for me... with the niggling doubt that I'm doing something wrong/should have made a different purchase/have dodgy eyesight etc etc!
Kirk, I had a look through your site. Gorgeous, amazing work. I know Santa Fe really well, once spent a month there but unfortunately only took shots with a Canon G4. However, some of them are printed quite large and look fairly good.. to me...