Now, I'm clearly totally biased, as I have a D610, but in my opinion the D610 is hugely under-rated and does, as mentioned, have somewhat of a stigma attached. Needless to say, I love mine and have no intentions to change body any time soon.
If you twisted my arm and made me say one thing that 'could be even better...', it's low light focussing - when it's really gloomy it does hunt a bit, so the D750 would be better for sure here, I'm sure. The tilting screen would make close-ups of those flowers and fungi much easier too.
Talking of which - true story - I was setting up my camera for a long exposure of a train speeding past - camera left at edge of track and fired by remote. I spent quite some time lying down next to the track trying to set the camera up and pointed in the right direction. I was disturbed by a "ahem, are you ok?". "Eerr, yes, I think so" I replied, slightly confused by concerned yet caring words. "Do you need to talk about anything? Why don't you come up here and talk to us?". Ahhh, I see - they thought I was about to end it all on the railway track. They had been watching me form the window of their nearby house. I told them that if I don't get the train this time, I think I will throw myself under the next one. We all laughed very uncomfortably and they really were less than convinced by my mental state, which I can understand. So, a D750 might have saved a lot of embarrassment. Anyway, I digress. I'll go now before the nurse checks on me.