Originally Posted by
shreds
In the Nikon range the D90 is the second from the top of the range crop cameras, whilst the D700 is ranged below the D3.
What does this all mean? Well there is invariably a trickle down of features through the range and equally the cameras become that much more affordable.
Since you started off mentioning the D700, it appears that you are prepared to compromise the idea of a full frame for the cheaper D90.
There are advantages other than the obvious one of $$$. Clearly you have a good idea of budget, but how important to you is the full frame? Beyond that you could have looked at the D300 as a cropped frame camera one step above the D90. The D90 is smaller and lighter which may be very important to you.
The ISO performance of the D90 is IS0 200-3200 range (100-6400 expanded), so from this I would personally always be looking to keep the ISO levels below the 3200 mark and possibly even going down to ISO 1600 max. Is this sufficient? How much noise are you prepared to accept?
One thing to remember though, check out the alternatives within your budget, ideally by hiring or borrowing one for a week or so, if you can't tell the difference, then that is where you need to stop upgrading for now and it will define the camera to go for.
There will always be one better, but if you don't need it then don't spend the money.