Part of what you are seeing is the extreme magnification of the 18MP sensor.. downsize the photo to the D300 resolution and the noise youa re seeing will go away for the most part. The problem with the high resolution criop sensors is , on a pixel level, it simply shows more than your eye would ever see. in print it isnt visible. The 50D taught me this lesson. Goo dluck with your choices.. Canon big glass for now is more affordable though i fear that may well change.
I'm a D300 user (don't call me troll please

) and looking to move to canon because of the price of 500/4 IS and 7D.
I see more noise at lower ISO compared to D300. Actually D300 has more noise than 40D. This was one of my complaint about D300.
Love this shot too
http://www.sportsactiondigital.com/College-Soccer/Winthrop-gardnerwebb/9843260_zFGeq#669300564_yjzqh-A-LB
The file size is 2300X1900. Is this cropped or resized?
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Thanks
Jemini Joseph
http://www.wildbirdimages.com
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Please forgive the typos! A great speller I am, a great typist I am not!