Edward Ingold , Feb 01, 2006; 08:33 a.m.
In general, you want 300ppi at the final print size. With the F828, the 8MP size gives you a little more than 300ppi in an 8x10, and 5MP gives you a little less. On this basis, 8MP would be the better choice. You can always resample for larger prints.
You may save memory space by taking smaller images, but those pixels are lost forever if you want larger prints in the future.
The F828 sensor is relatively noisy above ISO 100 (even compared to the 5MP F717). This is due partly to the small cell size resulting from cramming 8MP into a 4/3 sensor. Reducing the capture size will have no effect on this noise.
You can find a full review at http://www.dpreview.com/reviews/sonydscf828/