I don't own a Nikon ut I have a Sony Alpha 700 which supposedly uses the same sensor as the D300. Recently I upgraded to an Alpha 900. I normally print A2, that is 16.6"x23.2". At that size I'd say there is little difference between the A700 (12.5 MPix) and the A900 (24.5 MPix). The difference is there, all right, but not really visible in the prints.
I'd say that if you print about this size and below you should look at your technique. I don't think that the 18-200 is a top notch lens. The 16-85 VR may be a better choice. My suggestions would be:
1) USE RAW!
2) Learn how to sharpen
3) Use mirror lock up and self timer
4) Use aperture between f/8 and f/11
5) Consider to buy a normal zoom. The 16-85 from Nikon and the Sigma 18-50/2.8 may be good choices.
Now, the Canon 5DII is sure a very good performer, you won't go bad with that option but I'd suggest that you try to use what you have right now optimally before spending another lot of money.
I am so excited to be on this forum and soak in as much info as I possibly can, maybe you guys can help me with a dilemma.
As stated, I have a Nikon D300 with the 18 - 200mm AF-S DX VR. Overall I have really enjoyed this camera and I know I have only been on the tip of the iceberg with its capabilities.
I shoot 95% tripod mounted Landscapes almost always between the 18-40mm marks (on my lens). I rarely shoot over ISO 400, and I have only used the flash once or twice (for things I could have done with our P&S which is also where the other 5% of my shooting usually is at this point). I like to print my images as gifts for friends and family as large as I can while maintaining quality.
With my current setup, I am basically unhappy with the lack of detail in my shots as well as some noise issues. I don't know if I am just being unrealistic with my setup? If you all would like me to post examples of what I am talking about I certainly can post some images cropped at 100%. I plan on eventually purchasing a nice Full Frame body, like a 5D Mk II, in a year or so depending on how things progress and pan out. So here are my current options, as I see it, in an attempt to get sharper images in my price range (if I can).
1. Sell my 18 - 200mm lens and purchase something like the AF Zoom Nikkor 18-35mm f/3.5-4.5D ED-IF
2. Sell my entire setup and go with a used Canon 5D body and maybe a Canon EF 17-40mm f/4L USM or a EF 20mm f/2.8 USM along with another prime or a basic zoom.
So is there any input? Will I get better image quality out of the 5D with those lens choices? Will I get better image quality out of the 18-35 Nikkor, but since it is not a DX maybe the opposite will occur with the D300 Body? I know I am jumping back in time with some of the technologies with the 5D but I am not sure if I would notice at this point.