I bought my 7336 at Lowes ($109), and a friend has the 7424.
My 7336 indeed has the 6" counterweight, and my friend's 7424 has the 5" counterweight. We were very interested in comparing them when I got mine, and took notice of this.
I use a 5" Hook-It plate and 6.5" Meg's soft buff pads. Very little vibration.
A side note. On mine, the "off" label on the machine has allready lost all it's lettering, as well as the PC labels. (I think some of the plastic clear covers were missing, and one was loose so I removed it) I called PC to get new ones and the woman suggested that I write on the machine with a magic marker. Even the local repair center said that these parts were not available and that I should just take the machine back for a new one. A call to Lowes got me a better 800#, they were very helpful, and have told me that they will send new nameplates. The woman I spoke to the last time even offered that "if you're going to be bragging on our machine, our name has to be on it".