My advice: don't believe filmscanner.info, it's utter rubbish in the sense that everything not Nikon (that they sell) or Reflecta (that they sell too) gets a bad mark... I've got 2 KM 5400 (v1 and v2) along with a Nikon 5000ED, and the Nikon lags behind by miles, in terms of resolution, optics, colour accuracy, grainyness, digital noise compared to Minolta High End Scanners.
About your question, it depends if you intend to do BW or Colour mostly.
my experience is that Plustek scanner with Silverfast gives consistently superior scans for B&W negatives: more precise, less grainy. Real resolution is 3600dpi but needs to scan at 7200dpi (takes time). The nikon IV will be faster, can scan strips of 6 but with a resolution of 2600dpi or less. The plustek works 1 by 1, manual process.
To be honest, I kind of regret giving away my plustek: I've never managed so good scans, I suppose this is thanks to Silverfast.
ICE matters, and then the Nikon software works much better than Silverfast iSRD, which is even worse than Vuescan IR dust removal (yes, this is possible..). On the other hand, Silverfast is v good for negatives with the negafix database which helps achieving colour accuracy.
Focus: Nikon's advantage is that you can focus the scan optics. But I never thought the plustek was disadvantaged.
I had 2 Plustek scanners, from new, and both had to be returned for failed sensor. Reliability is not great, I advise taking a 2 or 3 years warranty.
OS / Service / Price:
Nikon Scan is no longer supported, nor will the Coolscan IV be repaired if it breaks.
Plustek still exists and Silverfast software supports new OS.
Price-wise, Nikon's sell for much too high prices, with respect to their real performance, imho.
Hope that helps