I remember seeing some huge nemoralis when I was much younger that looked as though they could have possibly weighed 7-10g. Of course, it's impossible to actually tell without weighing them, but hopefully if I ever come across supersized cepaea nemoralis, I should weigh them to see if such theoretical weights are possible.
I found a yellow-with-one-stripe on the platform of a local train station that is freakishly large. Not quite the one above but an easy 2nd. Luckily nobody had stepped on it! Had to take it home by train. Photos soon!