R261/2004 compensation applies to overbooking. No extraordinary circumstances event exceptions either. If you have a booking, show up on time, and are denied for any reason you are entitled to either reroute or refund AND €250, €400, €600 (depending on flight distance) compensation. Equipment changes such as A320 to A319 will result in DBC.
The regulation also requires the airline to seek volunteers. This doesn't appear to be happening (based on above two accounts). They should be very careful as failing to comply with the regulation can result in severe sanctions.