When I first started with a D80 4 years ago... I was a noob... the camera functions overwhelmed me... well, it took me 2 years to get better at handling the D80.
Not that I have mastered the D80, but after that 2 years, I thought it was time to move on.
Like the other replies in the thread, the D700 is a faster car, that reacts faster and better in low light and at "spinning" the lenses.
The first time I used the D700 was during a wedding shoot where the higher ISO allows me to shoot faster with lesser noise and with a faster lens. It is a luxury as it allows more room for "error" but does not make your picture better if your composition is not good. Like a rich friend once said, put all your money into buying the most expensive gear and the only variable that the picture does not work is yourself.
The faster car allows more versatile and greater speed on the field. If that's where you are most of the time, then perhaps a faster car is what you need.
But if you are dabbling into studio lighting, then the D90 definitely suffice, just find the right lens to go with it. Lighting gears then take a more important role.
Not that I have mastered the D80, but after that 2 years, I thought it was time to move on.
Like the other replies in the thread, the D700 is a faster car, that reacts faster and better in low light and at "spinning" the lenses.
The first time I used the D700 was during a wedding shoot where the higher ISO allows me to shoot faster with lesser noise and with a faster lens. It is a luxury as it allows more room for "error" but does not make your picture better if your composition is not good. Like a rich friend once said, put all your money into buying the most expensive gear and the only variable that the picture does not work is yourself.
The faster car allows more versatile and greater speed on the field. If that's where you are most of the time, then perhaps a faster car is what you need.
But if you are dabbling into studio lighting, then the D90 definitely suffice, just find the right lens to go with it. Lighting gears then take a more important role.