Nikon Body Purchase

I have been doing mainly avian photography as a hobby since 2006 using a Nikon D50 with the Nikkor 80-400 AF VR ED 1:4.5-5.6D. My plan is to do an upgrade to get quicker FPS and better low light results when shooting birds. At this point I think I have read too many online reviews and am looking for suggestions regarding a new body. My thought was buying the new updated 80-400 lense and keeping the D50 would not do much for my wants or even improve image quality that much so buying a new body and keeping the old current lense may make the most sense. DX seems to be the way to go but which body would be the best fit with this lense. My next outing with be 10 days in Newfoundland, Canada for icebergs; whales; gannets; puffins; etc. Any suggestions are most welcome and I appreciate the input. My current lense can shoot on an FX body but not sure if buying an FX body and using DX mode is a good use of my money. On a trip like this a second body is a good idea bearing in mind the age of my D50, so the time has come to make a new purchase.

I was very happy with my combo of the 80-400 and the D7000 (until I dropped the lens from my bag). I bet that it will make a great combo with the newer D7200 too. Do take care for low light shooting. Although the D7000 was hailed as an excellent low light camera, and does pretty OK when it comes to noise levels, detail loss kicks in heavily above 500-600 iso. I don't know the specs on the D7200, but be sure to check on detail levels at high ISO. For real good high ISO performance, I think that still nothing beats th full frame cameras.
FPS has stayed the same on the D7200 and isn't spectacular, but it worked for me even with BIF. I think you will suffer more from the slow AF of the lens in those situations.
what I do like about the combo is the great IQ, lovely bokeh and the possibility to create quite large crops from a well captured image.

I have a few bird shots on my website taken with this combo:
This photo and the 6 after that (click next in the top right corner) were taken with the D7000 and the 80-400 AF VR ED 1:4.5-5.6D.
Some other subjects with the same combo:
Dragonfly; Rock wallabi; kangaroo; Plant 'macro'