Ray, you may know this, but you will need some extension tubes to extend the ES-1 further from the front of the 60mm (you can get a set of generic threaded extension tubes and use step-up/down rings on the end to hit the correct filter diameter). The ES-1 is designed to go on the front of the 55mm Micro-Nikkor which has a slightly shorter working distance and the lens assembly is deep set from the filter threads as well. If you were going to pick up a macro lens for duping, you could check out the 55mm AIS or autofocus 55mm F.28 which should give you about the same quality and cost significantly less. I find that I can more or less equal the output of a Coolscan V with the ES-1, D800E and 55mm f2.8 Micro-Nikkor.
As I understand, I don't need an extension tube with a 60mm macro lens on a full-frame DSLR, according to the following website. But I do need a BR-5 adapter ring. http://www.scantips.com/es-1c.html
The advantage of an extension ring with the 60mm macro, such as the PK-13, is that it would allow me to get a greater magnification than 1:1 and enable me to to make a stitch of a 35mm slide, perhaps doubling the size of the file, and allowing me to extract more detail, if such detail exists on the slide, which is doubtful.
Some years ago when I was using Canon equipment, I bought the EF-S 60/F2.8 macro because it got rave reviews for being ultra sharp. I never used it much. However, whilst searching for it just recently, I discovered I also have a portable transparency viewer, the Visual Plus VP-5050V. I must have bought it about 15 years ago, or more, and forgot that I had it.
This transparency viewer makes it easy for me to experiment with the 60mm macro on my highest resolution Canon DSLR, which is the 15mp 50D. Because the 50D is a cropped format, I'm able to stitch together a couple of shots (or 3 shots with big overlap) to produce a file size of around 190 MB in 16 bit, which is pretty close to that of the Nikon D800.
Using the same slide that I used to compare the Nikon 8000 ED scanner with the Epson V700 flatbed, I've found that the unsharpened stitched image from the 50D is as close as matters to the unsharpened scan from the Nikon 8000 ED.
If one were to put a very fine point on it, comparing 200% crops, the unsharpened 50D stitch, after downsampling to the Nikon 8000 ED file size, is a tad sharper.
Since this stitched 50D image is indicative of the sort of quality I could expect from the D800E, I'm wondering if it is worth splashing out $500 on a Micro-Nikkor 60/2.8G ED. The advantage should be, I will be able get the same quality that the 8000 ED scanner produces, but with a single click; no need to stitch.
Furthermore, the absence of an AA filter on the 800E might produces results at 200% which are two tads sharper.
Another consideration is the significantly higher DR of the D800, compared with the Canon 50D. The DR of slides is not that great, maybe about 6 stops. However, the DR of B&W negatives can be as high as 11 stops. Using my 50D to photograph such B&W negatives would not only require stitching, to get the best quality, but also exposure bracketing. I think I've just talked my self into getting a Micro-Nikkor 60mm/2.8.