D700 vs. D800

Well. Isnt this the question for the last few months? Of course this wouldnt be a hard question for me if my income was what it was before i got laid of work, which it isnt. But i am hoping moving up from a DX cropped frame to a FX Full frame will help me generate some of that income ive been missing.

So. Do i do that with the older but cheaper D700, which is no slouch when it comes to a full frame body. or do i spend another 800$ to step up to the D800?

MP's
Do i NEED 36mp? No. i do not. i really REALLY wish they'd made it a 16 or 25mp body. But they didnt. Sure, 36mp will make a great image. but. 36mp also takes up 3x as much hard drive space, memory when working with the image in Lightroom/Photoshop, and now i'll have to buy 48gig mem cards if i want to shoot the same number of images i am now with my 16gig cards. and im guessing THOSE are going to cost at least 3x as much also.
Id be happy with with D700 in almost all respects EXCEPT it is ONLY 12mp, which is what ive got now in my D90. Now. That being said, ive never saved/posted/printed an image using 100% of the size of a 12mp image, the highest quality ive used for my 12mp images is 50% of that size. But, as i get better and hopefully start selling images, that could change.

FPS.
How often do i shoot on anything other than Single Frame? Hardly ever. Do i need the D700's 6fps? no. Do i care if the D800 shoots slower? no.

High ISO
I was thinking this would be an important advantage to the D700 since its a Full Frame 12mp sensor. But ive seen the images of a D800 @ 3200 ISO, and they actually looked better.

I think what it comes down to mostly is overall cost. The D700 is down to 2100$ if you can find a new one. That plus the grip might cost around somewhere around 2500$.
The D800 is 3000$, i think the grip is up around 450$. That and new mem cards and tax, looking at about 3800$.

But. Those D800 images will be sweet. I'll have much more room for cropping, which isnt something i have a whole lot of now. But i dont really shoot with cropping in mind either.