windows 7 - What is the correct method to apply various group policy settings to multiple groups of users?

What is the correct method to apply various group policy settings to multiple groups of users?

An example of the scenario:
Windows server 2008, domain "CompanyName".
Presume all users switch between all PC's with a roaming profile.

GP = group policy, GPO = group policy object, OU = Organisational unit.

I have two OU's inside my main Users OU, as follows:

CompanyName Users
    Standard Users
        UserA
        UserB
    Power Users
        UserC
        UserD

For Standard users I want Control Panel disabled. Which I can achieve fine by applying GPO to that OU.

For Power Users I want the background set to a certain picture. I can also achieve fine.

Here is where the problem comes in, UserA and UserC both use a program that requires certain firewall settings which I'd like to apply through GP.
Putting this GPO in the main OU (CompanyName Users) then filtering the users it can apply to, I presume would work. However is this the correct way to do it?

What is the correct/best way to go about this? Is there a better way to arrange my OU's?