Hi JS,
I'm in a selection process myself and I found the following website quite informative:
http://www.pocketgpsworld.com/handheldcomparison.php
When you go to the 'Read Review' link under the models, most of your questions -e.g. reading of OS gridrefs- are answered.
Wishing you a good hunt and we hope for more personal experiences of users in the field.
Cheers,
Jan