I did my best to pick reasonably comparable images (processing/crop/subject/etc); they are all some of my better images that I posted to Flick'r. Other than a controlled side by side test I can't do better, and I can't do that because I don't have a D7000 anymore.
But that's kind of my point... there's more to it than just sensor size. From some of my best pictures the images you chose (2 & 5) are both D7000 images. Used well a crop sensor is more than adequate and virtually indistinguishable from FF at small sizes. And, IMO, a "good picture" isn't really about IQ anyway...
But that still doesn't make DX as good, or better in general. I only chose those images based on a general quick glance, rather than any technical reasoning [they are nice pics btw, and does show the D7000 to be a very capable wildlife camera]
I'm talking ... outside of wildlife, outdoor, scenic ... just general use, or when you do need to pump the ISO, I prefer FF - I used enough cropped sensor bodies to know I do. I've had a Sony A200, Nikon D200 + D90 - and loved all 3, but was getting annoyed having to go to the LCD menus to change certain controls - also, I was never comfortable with any of them pushing the ISO - none of them felt 'right' in hand either - just not 'hefty' or solid enough for my liking. I did shoot gigs using the D90 up to ISO 3200 and grabbed some decent enough shots, enough to please the bands I was shooting for at least. But when I got the D800E I felt it allowed me to go a step beyond. I shot a band in worse lighting up to ISO 10K and even had a print done up of one shot taken at 10K printed up fairly large [exact size I can't remember, but poster size] for a friend who's a fan of the band
Don't have any examples of that range on Flickr, but did post up a few, it was the first gig I shot using the D800. This one was ISO 4000. And I know if I was using my old D90 I'd have not got the same result, not even close.
Y&T, Pick flick by
Cagey75, on Flickr
How this helps OP? well, I guess I'd stick to suggesting the D610, because I feel you do have more scope with an FX camera, I do think they are better in every way - we're talking D610 Vs D7100 here I guess. They may be built very similarly but the D610 gives you more of an edge, in almost every situation. The dynamic range, the ISO performance, the crop-ability, I'd add build quality but they're probably not all that different in that sense? But if he went for a used D800, which i suggested to begin with ... you get that on top too.