The lighter and smaller 350 might be an advantage if you are using it piggybacked on another telescope. For what its worth I love my 300D for daytime and astro use. I havnt compared it with other cameras side by side but in day time use the lens makes all the difference especially for wide angle. From what ive heard many people seem to think the 350 is the best in the series for astro use. My next dslr will most likely be a full frame one when they come down in price.

Alex