I just finished detailing my GD3. HOLY SMOKE!!! Now I remember why I was being lazy about not trying to detail it. Wash, Clay bar, Wash, Wax, Wax, Wax... I'm using the 3 step from meguiars and love it. The car is glowing like a damn mirror. I love the way it comes out. ANyway, HEY QB!!! You do an awesome job man. I was checking out the cars that you've done and boy ole boy, they're awesome. Good job man.

 

I use the same setup regularly. 5.5" is my regular use pads, but I also have 4" and 6.5" (mostly for rotary use).

 

For a porter cable 4" pads are best. Since the porter cable is so much weaker than a rotary buffer, the smaller diameter of the pad increases the heat and friction over a larger size pad. Using a 4" pad gives you more cut, although it takes way longer since its so small. For rotarys its usually best to use 6.5" pads. I use 4" with my porter cable for my honda details.

 

I agree the 4" pad will create more heat and cut, but over all I prefer the control I get using a 5.5" pad. It all comes down to preference when detailing cars (technique and product selection).