Well it depends what ISO is being used. If a low ISO (100-200) is being shot with the Digital Rebel...there should be no real lack of IQ. It's proven fact that noise and IQ are negligible at low ISO's throughout most camera manufacturers camera body lines. Raw files shot with the same lens under the exact same lighting conditions with ISO 100 on a 5d and a Digital Rebel will look close to identical. You may be able to differentiate slight variations in colors, but noise will be identical, and IQ differences will be invisible to the majority of pixel peepers (and pixel peepers alone). Reviews all point to this. Now as soon as you start shooting above ISO 200 on a Digital Rebel your quality will deteriorate compared to a 5d due to the pixel size and density (Duh we're comparing FF and 1.6x crop). Either way there shouldn't be "poor" results at low ISO's with a Digital Rebel. I've seen spectacular photos with Digital Rebel's and fantastic photos with 5d's...really it comes down to the photographer 😉 It all depends what the Op's shooting. If shooting low ISO, a new camera won't necessarily make a large difference, if shooting medium to high ISO's, a 5d will blow away the Digital Rebel. I would recommend a new camera as well at this point, but I wouldn't just jump on the bandwagon saying "it's more expensive, it's a better camera". There's so much more science that goes into a sensor that makes the difference. Compare pixel sizes, densities, FF vs. crop, sensor capabilities, and processing power within the camera.