implementing multisite security groups

I would like to know how best to implement security in following scenario.

There are 5 subsites, US,UK,India,Japan,China in a sitecollection. Each subsite has further 10 subsites under it like HR ,Marketing,etc.

There are 5 security group levels to which a user can be added.

For e.x., User A can belong to Security Group 1 in Subsite 1 of India. He can also belong to Security Group 2 in Subsite 2 of India, He can belong to Security Group 1 in Subsite 3 of India.

By this, I find that the total number of security groups to be added is 5 security group levels  X 10 Subsites X 5 top level subsites = 250 groups. Is there any way to make this better?