Permissions and Groups on a New Server
Solution 1:
775 is okay, it just means that it is group writable/cd-able and world readable/cd-able.
It looks like you already did a chown user.sharedgroup and chmod g+s where the writes take place to ensure that the files created there are owned by the common group.
Permissions like this are acceptable when they're well-thought out, understood and documented. I don't see any problem with your setup.