Chrisn, Consider the Garmin 276C, its the smallest of the marine chartploters and has a screen the same resolution as the Quest but is 3 times the size, it also does a lot more, it has the fastest processor of all Garmins in common with all the chartploters and is absolutlely waterproof.
The unit does not come with any software as it can use Bluechart, Mapsource and topographical data, you choose the application, the automotive kit comes with V7 mapsource and 256 Mb chip and lots of other bits.
In the US this has been replaced with the 376C which has the ability to recieve weather data and display it over the top of the maps, unfortunately it only works in the US.