While I'm in the process of going back to my 4x5, which I haven't used for about 20 years, I really don't recommend it for "model shoots". While I'm returning to it, I find that each time I click the shutter it costs me between 2 and 3 bucks for B&W. I'm returning to it for artistic purposes. I strongly recommend the RB or RZ 67 and absolutely love my RB. It's a solid work horse. needing little maintenance and because so many are available on the used market (KEH.com), prices for the bodies and accessories are reasonable. I'm down to one now, as I found they don't bounce well off of cement floors. It will also be outstanding for the chromes you shoot for stock.
A month ago they had to call the paramedics when I was given the price for one which would scan up to 4x5, so I bought a 400 buck Epson2450. It does a wonderful job, but takes about 6 minutes to scan a 35mm neg or chrome to 8x10 at 300 ppi. That's before the time needed to work it in P'shop. So if you are unhappy with your Nikon scanner, I'll be glad to make an even swap with you. I've bought cars for less than the Kool scan price!
Based on what you said, I do think your problem is in the scanning. Sounds like investing a few bucks in a guru might solve your problem. Actually, I've also found that loading the image, after corrections, into a non P'shop program can help to find flaws. I use a Mac, so the programs might be different for a PC, but I use iviewmultimedia or jpegview as a final check.
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