Klaus,
The following is just opinion, not based upon actual use of either digicam.....
From what I've read, as long as the physical dimensions of the sensors in question are about equal, I would not necessarily conclude that 5 megapixels are that much better than having 4 megapixels. There are other factors, such as chromatic aberration, that come into the discussion. It also depends on what your plans are for the final product. Unless you are planning to enlarge prints of your images well beyond 8x10 inches ( sorry, i'm too lazy to convert to cm's), the extra one meg may be unnecessary.
Another consideration, IMHO, is that both of these cameras have only auto exposure control, without the option of setting manual shutter speed or aperture. One of the digicams even limits the ISO setting to Auto. The images I've seen posted in the past from digicams with similar features lack certain aesthetic qualities and are prone to motion blur. Unfortunately, this group of cameras do not determine exposure settings as well underwater as they do above.
I've based some of my observations on specification information I reviewed at dpreview.com. You may also try imaging-resource.com and steve's-digicams.com for comparisons of which digicams may suit your needs. For available housings, try digideep.com.
One other point to consider is if you plan on adding a strobe, tray and arms.
