Thanks for the replies folks!
Expert or not, its good to bounce ideas around with people who at least have half an idea!
£150 cashback on the D600?! Doh!!!! Although I'll have to look into it to see what the cashback is on... if its any old camera, that might work! If its an SLR, hmm... then I might need to buy some old body off Fleabay.
However, on the FX vs DX debate, I'm a bit ambivolent on it at the moment. I like the idea, but haven't used an FX to see the differences in practice. So I'll happily stay DX if the camera has the milage, and that makes life cheaper! I guess at the moment I'm a bloke looking for the next new gadget and, until it actually comes to really looking at honest budgets, the D800 looks great!
However in reality, my D90 IR conversion will be £250, so that will knock any budget I might have.
So, if the D600 problems have been "fixed" (or there is at least a process in place to deal with them) then that puts it back on the table! Although the crop mode won't be as good as the D800, the price difference might allow some glass.
D700.... hmm... someone at work has one and loves it and there seems to be a fair few of them on Fleabay, although prices do seem quite high for second hand... hmm...
D7100 not to market yet? Ahh, that might delay the decision a little, or maybe not...!
May take a run into town tomorrow and see what they've got....