Nice pair there.
I have the D90 and for lenses the:
- Nikkor 50mmf/1.8
- 16-85mmVR f/3.5
- 70-300mm VR f4.5
Out of the three of them, the 16-85 and 50 take some incredible pictures. I have found that I am not overly impressed with the light speed of them. The 3.5 and 4.5 are very limiting, especially when you get to the long end of the lens.
The 50mm is just too long to take some action shots within 15 feet. It does however make a wonderful portrait and walk around lens.
As such, I am in the process of trading both of my tele-zoom lenses off on Tamron f/2.8 glass, the 17-50 and the 70-200. I will be adding the 1.4X teleconverter eventually.
I tried the Sigma (Quantary) 70-200 f/2.8 lens today and talk about a heavy lens compared to the Nikkor 70-300. Something you REALLY want to have to carry for what I will be wanting to use it for. I go out really early in the morning either before the sun comes up, or late in the day when it's going down. The f/4.5 glass has me stopping before I am ready to. Just as the wildlife seems to becoming alive and moving.
I also take indoor sports/action shots where flash is not allowed. Even running at ISO 1250, I needed to run an aperture of f/2.8 and f/3.1 to get some decent stop action shots. Fast enough to stop a swinging wooden sword.
Because of some of the comments regarding the zoom helical's on the Sigma/Quantary, I held out and am waiting for them to get the Tamron 70-200 f/2.8 in. I really like the options with the lens, and am looking forward to it.
I did try the 17-50mm f/2.8 today and it's now sitting on the shelf with my name on it, waiting for the 70-200 to come in. Once they are both in, I will be trading my Nikkor slow lenses for the Tamron Fast lenses.