A drill with 4inch pads will give you the most cut by far.
Some spot buffing kits come with a backing plate that can be used to work with a drill and a PC. Go with that and some cutting pads and you'll be sweet!
Also SSR3 isn't very good at cutting with a PC, its definitely rotary only. In my opinion
Meguiars M105 will cut nearly twice and its much more PC friendly.