Thanks to many for good input/feedback--here are some of my early conclusions based upon some controlled tests. Standard Disclaimer, of course, YMMV:
1. It is indeed worth scanning at 48 bit RGB vs. 16 bit grayscale. Very noticable difference regardless of scanning software--48bit RGB scanning is preferred in my workflow/system going foward.
2. Silverfast Ai provides better scans consistently than Epson Scan in my workflow/system in every comparison. Very noticiable.
3. Compared three prints from each channel. Kirk, good call, green channel is the way to go with the 4990. Green is slightly better than blue.
4. Channel mixer vs. just the green channel are the same if R/B are dropped to zero in the latter. Thanks Frank/Jeremy for your feedback regarding channel mixer. At first, I was a bit apprehensive due to what I perceived as a lot of tweaking. You comments persuade me to take a closer look--
5. Green channel or channel mixer provide slightly better results than going into LAB mode and deleting (B and Alpha2 channels). Better depth overall. From a color workflow perspective, I like to apply USM filter in LAB to minimize abberations/artifacts. Not sure if this applies equally to B&W? However, I don't think going with a non-optimal b&w conversion process is preferred over workflow time.
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