I picked up a 120 white and 80 yellow grit 3m Bristle Discs for my 4 1/2" grinder ($60 shipped). In the first few minutes with gentle pressure on the front/underside of the hood (where rust-through was/POR15'd long ago - rust all gone), I lost the outer row of bristles on the 80. Moved on to my driver's side fender extension, and got down to bare metal fairly easily, but the bristles look more worn than should be for such a small effort. Anyone able to give an idea how long each disc will last? I'm thinking it would be much better to just buy a big bucket of paint stripper to pull off the paint layers, leaving the base primer layer. The paint/powder in the air was nasty to smell hours later. Eric.