If you were me?
The 5DmkIII has more pixels, a lot more, but noise is more or less the same.
You can see for yourself with the DPreview studio comparison tool.
Buy some nice glass
Scott in St Louis wrote:
There are thousands of posts that may address this, but I'm hoping some kind hearted people will just indulge me.
I hate ISO noise. I'm a Nikon shooter, but I DO NOT have any expensive glass binding me to the company. I have a D700 which is working just fine. I read the PP review of the 5dM3 and was blown away by their noise numbers. I read their methods, and they use DxOAnalyzer to test and assess noise levels. The 5dM3 doesn't get to "moderate" until 25,600 where as the D700 gets there at 6400 (old review). However, if you look at DxO's web site, they say they are essentially the same in terms of noise. Who should I believe? It's hard for me to interpret these things consistently.
The frame rate of the D800 is a non-starter for me, so I'm not even considering it. Mostly shoot kids sports, and some portraits.
My question is, should I double down on Nikon, buy some good glass and hope they come up with a reasonable upgrade for my d700 in another 3.5 years, or should I change teams and go with the 5dm3 and it's potential for higher ISO performance.