I use Lightroom as my primary editing software for all film scans (TIFF) as well as the few digital images I've shot of late. I find it far easier to do basic adjustments in LR, and need to resort to PS only for extensive or complicated dust removal, which the Spot Healing brush in PS does much, much better than the analogous tool in LR.
Most of my film images are 6x7cm scanned at 1800-2400ppi in a Nikon 9000 or at 3200 with an Imacon 646; or 4x5 scanned at about 2000ppi in the Imacon. This makes for some rather large files, though not as large as yours. Performance is decent on my MacPro 2.7GHz with 14 GB RAM. Generating previews especially at 1:1 takes some time, and occasionally (if the computer is doing other stuff too) I get some lag moving the sliders.
Cataloging duties are shared between LR and Expression Media 2, though I'm gradually shifting more towards LR, given the lack of clarity about MS's intentions for further EM development. I can only hope that future iterations of LR preserve what LR does well, and improves those DAM things that EM does far better.
Just curious: why do you need such high resolution scans? are you making enormous enlargements? There is a considerable school of thought that scanning at those resolutions---depending of course upon the scanner---serves mainly to accentuate grain and imperfection, without adding appreciably to final image quality.
I use LR or occasionally acr to manage my film scans. I find the masked sharpening can be useful as well as the develop module's tools. I only scan 35mm at present using a nikon 5000 and the files are similar size to a converted tiff from my 1Ds3. (Like you Mike, I've not shot much digital lately and have considered going to 6 by 7 for more static work)
I am interested in the scanning resolution questions, but my sense with the Nikon is that even scanning at lower than max resolution doesn't change the hardware high frequency response so any grain aliasing remains.
Attached scans are from a nostalgic roll of Kodachrome.