Gawd, I was hoping for a resounding yes, luckily I waited. The two lenses were a Sigma 17 - 50 2.8 and Sigma 10 - 20 3.5. My main problem is noise even at relatively modest ISO's (e.g. 1600) and I was hoping the 750 would help with that. a used decent nick D500 is a good £300 extra currently so I guess I'll stick with what I have and wait and see what the D7500 brings. Thanks for the advice, saved me 600 quid.
I have done airshow work and if the D3000/D5000 series 24MP sensors are anything to go by,I found my D600 seem to do far better in every way once the light started dropping,and they seem to have far more latitude too especially when it came to shadows. The main issue is the reach,but many of the airshows in the UK tend to verge towards crap weather towards the end.
Its the same with some of the landscape stuff I have done while hiking up Snowdonia,etc and at sunset/sunrise when hiking up/down,the D600 I found not only had better DR,but I could use higher ISOs when taking pictures and DR is pretty decent too despite this. This is important as the light can change very quickly and people who tried to wheel out all their tripods,etc usually ended up missing it all. Would a tripod be ideal,probably,but its not always the case you have the time or space to set up one,especially if it is more a general trip,as opposed to a fixed point photographic one.
The thing is though the D600/D610 and D800/D810 have been out for a very long time,and the D750 is basically a newer version of the D600/D610 with probably the same(or a slightly newer version of the same) sensor. I would suspect,Nikon will be updating those lines in the next year or so,so it might be worth seeing what these bring to the table.
They have already updated the APS-C and professional FX sports line,so these are the next models which need to be updated.