Thanks for your help Mix, I've decided to go for the 6 plus because I use it as a sat nav in my skip lorry and the bigger screen is a distinct advantage at my age !
Security isn't an issue because I remove it from the truck every time I get out and I also have a snappy little Jack Russell who regards the truck as his mobile kennel and is not to be messed with, your advice is much appreciated Mix, cheers Stuart.