MR, I think a lot of the confusion that I see here is the conflation of digital camera stuff with printing stuff (your newsletter print shop guy and his requirements).
Terms such as a "raster graphic", RGB vs. CMYK, and even the 600dpi that you reference are way more toward the print shop side of things than the digital camera side of things. They're stuff that your printer is interested in (and, by extension, you are for your newsletter) but don't have much if anything to do with your camera - but, instead, with how you prepare your newsletter for printing...and how he deals with it after you deliver it to him.
(For the record, a raster graphic is a scalable graphic (think fonts here - it's math that renders pixels rather than a map (picture) of pixels), RGB and CMYK are ways (color models) that offset printers deal with colors (Red, Green, Blue and Cyan, Magenta, Yellow, and blacK). You've heard of "four-color offset printing"? The printer (theoretically) makes four passes (one for each color - CMYK) to produce the full-color photograph (or a photo in the newsletter). It's just a printing technique and doesn't have a thing to do with the original photo nor its format. And the 600dpi or 180dpi is the resolution at which he'll print - or wants to print.)
Also, neither of your cameras has the capacity to shoot in RAW mode. They will only create .jpgs (and there's not a thing wrong with that). I would, however, set both to take the larges pictures possible...fine is how it's described in both manuals. It's lots easier (and way more effective re quality) to decrease the size of a photo as needed than it is to increase it.
Again, I think simplify is the key here. Shoot high-resolution photos (finest of the fine on your Canons). That's all that's happening in camera land. That's the product that you produce with the camera. The rest happens elsewhere with other software/hardware. Converting the .jpgs to TIFFs (and converting from RGB to CMYK at the same time using the same program) - if that's what the printer needs - are steps into print shop land.
