I have the 805, so here is my input....
The 805 has plenty of power. The wattage rating is WPC for all channels, not for two channels. I have a large family room, and it fills it quite nicely.
for the 1080, 720 issue, HDMI passes the signal straight through in the same resolution. If you are running component cables, and you are willing to not have the sooooo nice "just one video cable" to the TV, you can run the component to the TV instead of the amp.
Many will tell you that you cannot really see a huge difference between 720 and 1080 unless your screen is larger than 50". I have a 50" Pioneer myself, and I cannot tell the difference. I used Y cables, and have my component cables going up to the TV, and through the amp. I sit at about 12 feet away. Others would disagree with me. Your eyes will have to be the judge.
If you google it, you can see the chart with screen size, resolution, and seating distance and base your opinions accordingly. My eyes agree with the chart.
One last thing....everybody here that has the 805 loves it. The Aperion Gurus know Onkyo very well. One of the many great things about them is that they not only help you with your speakers. The are always willing to help you dial in your electronics, whether you bought it from them or not. Their service is second to none.
Good luck!
Scottiemon