Service like "Opera Max" for OS X?
An interesting idea, but I don't think such a service exists for OS X. There would have to be a complementary service on the other side of the internet connection to uncompress the data, which is what the Opera Max service does for Android users.

If you read the Opera Max FAQ, they write that... "We're working hard to bring Opera Max to new regions. To ensure a high-quality experience, we have to buy, ship, and set up new servers all over the world."