HI Ed, it just does not rely on the scanner alone. As long as the scanner is well maintained with a clear optical system at least the technical part should be perfect. However, the other – crucial – variable is the scanner operator. It requires more than just to throw in the slide, push some buttons and yell ‘finished’. I know several drum scan operators, but only a handful delivers perfect results. Same story with ‘virtual drum’ scanners like the Imacon and the dedicated Nikon LS 9000. I’ve had scans from my LS 9000 that easily beat scans (from the same slide) from a drum scanner in terms of sharpness, resolution, color rendition and contrast.
If you have subcontracted the scans, you didn’t need to know the parameters.
Using a flatbed scanner is a totally different world which can’t be compared to dedicated film or drum scanners.
I’ve added a real world example here