I am looking to upgrade from a Canon 400D to Canon 600D body only or another camera with similar specs/price. Main reason is i can't stand the noise in the 400D. So my question is how does camera noise nowadays compare to 4 years ago? Are the improvements significant enough to justify an upgrade? The noise graphs on dpreview don't seem to suggest much improvements, but i'd like to hear the views of people here.
I will be attaching a permanant light blocking filter to the lens, and will be using high iso (1600 onwards) at long time exposures (> 4 min), so i'm mostly concerned with noise levels under those operating conditions.