Dpreview.com has side-by-side shots of the Canon S5 and the Sony DSC-H7 at
80 ISO,
400 ISO,
800 ISO, and
ISO 1600 so you can look at the differences and decide for yourself.
I would also recommend reading their full reviews for the
Sony and
Canon cameras as well.
When shopping for a new super-zoom a year ago, I narrowed my search down to the Sony DSC-H7, Canon S5IS, Panasonic FZ-25 and Fuji S6000fd. AFter a lot of research and comparison of features that matter to me, I ended up going with the Fuji. It might not matter to you, but the Fuji has a more pro camera look at feel to it, and I love the manual zoom ring on the lens. It also does quite well in low light situations, although still nowhere near the class of a true SLR.
In my opinion, the two primary drawbacks to the Fuji are that it is a shorter zoom than the competition (10.7x) and there are times when I'd like more zoom although it does have a wider short angle than the others which helps a lot in close/portrait situations, and it doesn't have any optical image stabilization which is a problem for some people at long zoom lengths although it doesn't bother me much since I have very steady hands. It also uses the annoyingly expensive xD picture cards, but you'll have the same problem with Sony's Memory Stick Duo cards. The convenience of being able to pop in a spare set of AA rechargeables (or common alkalines) makes up for that for me.
On the other hand, one thing that I really like about the Fuji that none of the competition have is the ability to shoot in RAW mode, which when combined with proper processing on the PC can result in dramatically better image quality. The LCD is also (in my opinion) MUCH better than on any of the other cameras, mostly because it has double the resolution of the other cameras. The EVF (electronic viewfinder) is pretty bad on all four so I just use the LCD most of the time.
I probably didn't help you narrow things down any more by adding two other cameras to the list, but if it helps, to make my decision I made a list of all of the positives and negatives of each camera and weighed them against each other to find the camera with the most things I liked and the fewest number of things I didn't like. In my case that was the Fuji S6000fd. For you it might be one of the other cameras depending on what is most important to you. For example, if you really need that long zoom, the Sony and Panasonic are hard to pass up. In low light/high ISO, I think the Fuji is the best of the four with JPEG images straight out of the camera, and when you use RAW images and good post-processing, there's really no comparison at all.