Well, you picked the right card at trying to unlock the extra four pipes. The Powercooler 9800SE is supposed to have the highest rate. However, that high rate is only about 50-60 percent. So basically you have a 50-50 chance of softmodding this card into a 9800 Pro. About half of them artifact on the screen when you unlock the extra four pipes.
Having said that, I wouldn't go the refurbished route. More than likely most of these are cards that were unsuccessful at unlocking into a 9800 Pro and they were RMA'd back. If you go with a Powercooler 9800SE I would go new.
Otherwise just spend the extra money on a 9800Pro. You can get them for about 200. Otherwise you could get a 5900XT. Those go around 175-190. If you go the 9800 Pro route, make sure you get one which has a 256 bit memory bus. There are some 9800 Pros around 170-180 bucks that are using a 128 bit memory bus.