I have a 50PX600 and OPPO 970. My knowledge is what tdavis21484 said. You might check out the OPPO threads on the (Non HD) DVD player forum. Some say that the Faroudja chipped 971 and 981 soften the image a bit too much in comparison with the 970. I'm very happy with the 970. I'm also waiting out the HD-DVD war, but I'm afraid it's going to be a draw.
ps The 981 is probably worth the 30 buck premium over the 971 because of the extended format compatibility.