rightwaway- What you need primarily depends on the paint in question...not its *color* but rather its hardness/softness.
Different products had different types of abrasives (larger/smaller, sharper/duller, diminishing/not) and different types of carrier agents (oils/lubes/etc.). They're simply *different* (often more just plain different than "better/worse") and some people like one thing and others another.
I've never used that Pinnacle product, so I can't comment on it. But I can say that if M105 doesn't do a job, then that job probably shouldn't be done
You might also look into the new spray compound/polish from Optimum. I haven't used those either, but I bet they're great.
IMO that 6" pad is a waste of time. Yeah, smaller would be better and while some like 5.5" pads I go all the way to 4" for correction via PC.
Sorry, no idea who has good prices, I shop more by service than pricepoint :nixweiss