For those of you who have never worked with Nikon's NX software, I'd like to suggest you try it with your 5D II files once they've been converted from RAW in your usual way, whether you convert to TIFF or JPEG ... or whether you shot JPEG to begin with.
NX has features and adjustment ranges that are extremely well-suited to the 5D II's files. NX's full feature set will work with any JPEG or TIFF from any camera. Some of NX's "base" adjustments will only work with Nikon RAW files, which is to be expected. But, beyond that, NX is an all-purpose program for dealing with digital files in a way that no other programs quite match. If you've never used NX, you'll see that it doesn't at all resemble ACR, RAW Developer, Lightroom, etc.
There's a steep learning curve with NX, and it can be painfully slow at times (as well as a little buggy). But I think the end result is well worth the investment of time and money ... although I'm sure there are NX haters out there who will disagree.
I process all of my JPEGs in NX, regardless of camera used. I've just "re-processed" three of my 5D II files via NX that had originally gone through DPP, Photoshop and/or Lightroom. The improvements are noticeable and welcome, particularly improvements in color and sharpness.
I'll try to post some comparison pics at another time.
More importantly, have you compared them with well processed files from C1? That's currently the benchmark for many for absolute top IQ, with the benefit of being able to process the actual RAW files, not just baked Tiffs.
C1 used to be the top for IQ, but I haven't found that to be the case for a few years. I get more noise and edge artifacts from C1 than ACR, and I find Canon's own RIT is even better than ACR.
I too would like to hear more about what was done with NX.