There aren't many cameras you could use to image Jupiter/Saturn that would also double as a DSO imager... In fact, I know of none (appart from a long exposure modified webcam, but even then, if you're looking at an LX200 10" A LX webcam is a pretty measily toy to be hanging off the back...
For Deep sky imaging, you cant go past a dedicated CCD.. The 40D is a stupendiously good camera, but for astro-photography, having it modified is nearly a pre-requisite, as the standard IR blocking filter is fairly heavy handed, and blocks alot of very useful wavelengths... Don't take that the wrong way, There are of course, many many people taking excelent deep space images with DSLR's. But most of them (I imagine), given the choice, would jump to something like the QHY8 or ST-7 in a heart beat.
If I had the choice between those two specific cameras, It would be a hard decision... The extra resolution of the QHY8 makes it jump out as a good option, however it being One Shot Color (OSC) would likely make it alot less sensitive, requireing longer exposures, putting more emphisis on a having a good mount capable of tracking for long exposures. The ST-7 (depending on which model ST-7) has dual sensor.. making it self guided, removing the need for a dual scope setup with yet another camera for auto-guiding...
I would probably go with the QHY8 all things being equal... but mainly because I love the images they produce....
Hope this has helped a little...