So autogeek is have a 15% off sale this weekend and I decided to buy a Porter Cable 7424XP. The problem I'm having is that there are several kits to buy. Some come with a 5.5" backing plate and 6" pads, and some come with that plus a 3" backing plate and 4" pads. I don't know which kits to go for. What is the reason for using one pad size over the other?

 

smaller pads are usually for tighter areas or spot buffing. For example, the back of the trunk around the "H" badge.
I use both but rarely use the smaller 3" pads/backing plate.
You will be happy with the 5.5" pads.

 

here is some Uber 5.5 inch pads

make sure you have a 5 inch backing plate.

 

From what i hear 5.5 is easier to use.. but i wouldnt know since i am a noob. i ordered the 5.5 pads..

 

on a DA, a 5.5 is about the largest youll want to use. the small 4" pads do come in handy many times for the tight areas and for spot buffing.