Ska I have these same symptoms. It used to judder a while back.. but then went away. Just recently its back, pretty well noticeable all the time at about 65-70, then will go away.. come back..first of all felt like wheel balance, but I recently had them all balanced when changing the wheels over so not that - definitely notably worse under braking, to the point where when the car is coming to a stop and I have my foot on the brake pedal, I can almost 'feel' the pads grabbing a bit.
Warped discs I am thinking.. hence the other question about which discs to get (I think I have the same setup as you so will be looking at 345mm - any rough price I should be paying)
Anyway will watch out for all this although dont' think my calipers have been painted at all. I'll make sure the surfaces are properly clean though when I get to changing the discs.