I have found today after a number of unsuccessful searches some sample scans of the new Canoscan D2400UF, announced at 2400 dpi optical resolution and $500. Here is the adress: http://www.myalbum.ne.jp/cgi-bin/a_menu?id=fa268931
This page (in japanese unfortunately, but the captions are in english) in is very interesting, as it has some samples of 4x5" slides scans (taken with good equipment: Linhof Technika and Nikkor lens), together with 645 and 135. It shows what the Coolscan 4000 from Nikon does with small format too... impressive !
I am not (to say the least) particularly impressed by the results of the D2400UF. The scans are *very* unsharp, and though I know that sharpening in Photoshop can help a lot, here the high frequency modulations (i.e. the details) just seem to be absent and not only dimmed. Therefore, impossible to recover...
Currently I am using an Epson Perfection 1200 scanner, and I am relatively pleased with the results, but the extra resolution would be interesting, especially at $500. After seeing these scans, I am not sure now if there is an advantage to go for the Canon.
By the way, there is also a few other samples at the adress: http://www.geocities.com/aanticulturee/scantest.htm
I would apreciate any comment you may have about this question, and which scanner in the sub $1000 range is be your favorite for 4x5".