Hi Justin,
You are getting some nice results but this one I think needs more data and less blur as it doesn't show much structure, just my opinion and I'm no expert.
Are you able to retain the 12 bit format while editing? I know 4 bits aren't too much but it could enhance transitions in subtle areas.
for eg, 12bit to 16bit does have quite a difference in the number of shades of gray.
PS CS5 supports 16 bit, so I presume would support 12bit native.
also, i'd suggest against using gaussian blur and to instead use dithering and darks to remove noise. the blur would remove a fair bit of contrast in areas with sharp transitions. dithering and darks are very effective with noise reduction.
this was an image i found with 5x20min subs with a cooled dslr so not a straight comparison, but i just wanted to highlight the dark areas that make details stand out if you know what I mean.
http://www.centralds.net/cam/?p=2269#!lightbox[auto_group1]/0/
Look forward to more.
Cheers
Alistair