I actually agree more with Mike. Already having the 300D the webcam (being the perfect planetary imaging camera) would complete the package better than a DSI would.
Also imaging Jupiter with a webcam requires much less precision on the mount's behalf than imaging a series of even 30 second exposures with a DSI. You might end up just getting frustrated with the DSI because of the relatively long focal length of the 8" and small pixels size, resulting in it being hard to get nice sharp non-trailing images.
In contrast I know people who get great images of the planets with webcam's on very incaccurately motorised DOB's.
Roger.