I've used 7day for high quality (Ł10/36 exp 35mm) scans equivalent to 6MB. They seem good at about A4 - although I haven't tried larger. Only thing is that if I have a set of the same subject, the one I like best seems to have a blemish! I think they usually scan from the roll, but sometimes they scan from processed slides and at least once must have dropped the lot as the images came back upside down and generally jumbled up. They respond to questions promptly and thoroughly and I give them top marks for processing/scanning/printing.
I suspect some processors scan from prints with dramatic loss of quality.
I'm looking at film scanners as a way around the problems but there's a lot of conflicting data out there. Maybe I should stick with 7day and take two frames of everything!