Kev,
I used a Nikon 8000 with 617's and scanned the transparencies in two halves and matched them in 8 bit Photoshop layers. This worked fine except that sometimes I had trouble with scans where the picture was dark on one side and light on the other. In this case the auto exposure in the scanner messed up matching the two scans. However a lot of messing around in Photoshop would make the scans useable. The contrast range of the Nikon was not bad but not as good as the original.
I bought an Imacon 646 (because I also use 4x5) and it is brilliant, the contrast range is incredible and you are hard pressed to tell the difference to the original. The Imacon FlexColor software is excellent and you can do almost everything you want in color control and "sharpening" that you can in Photoshop. The advantage is that you do all this work before the image is scanned and so there is minimum image degridation (if any) and the details of the adjustments are saved with the file in 16 bit. Photoshop does not do this as layers have to be in 8 bit. Imacon FlexColor will also scan in a proprietry RAW mode (Imacon .fff) and the new Photoshop RAW converter will open these into Photoshop 7.0 (if you would want to do this) however you can continuously re-import the RAW image into FlexColor, manipulate it in the RAW state and then save it as a TIF, while saving all the adjustment details in the 16 bit RAW file.
If you are influenced by my comments on the FlexColor software I would check to see if the software supplied with the 343 is the same as that supplied with the 646 otherwise my comments will not apply to the 343.
I personally think you cannot go past an Imacon, as far as I know all they make is digital imaging equipment and it is the best scanner I have seen and as good as the drum scans I have had made from time to time. I also believe Michael Reichmann uses an Imacon FlexTight II and has a review on this site.
Frank