What's the most optimal video resolution setting for a Panasonic TH-50PX75U? It's native resolution is 1366x768 and it always says (720p in parenthesis). I have a Motorola cable box and an Oppo 981 DVD player, and I can choose 1080i or 720p with both. The TV is 50" and I sit about 9.5 feet away. I've tried both, and I'm not sure I can see a difference.