The Panny would be my choice for a 720P at 120". The only other one might be a Marantz 12S4 with long throw lens option if you can find one but 120" would be pushing that PJs brightness but 100" would be fine. The smoothscreen will help you at 120".
The 720P vs 1080P has been a long debate. I evaluate and calibrate a lot of PJs and I wouldn't take a lower cost 1080P over a higher end 720P. Because contrast (ON/OFF and ANSI), color, saturation, etc. are bigger factors than resolution for picture quality unless you are sitting close enough for screen door to be a problem. A lower end 1080 display will usually beat a lower end 720 one, and a higher end 1080 will usually beat a higher end 720. The only time that 720 beats the 1080 is when the higher end ones have been discounted to the price range of the lower end 1080s.
As far as broadcast signals go there are tradeoffs between 720P and 1080i. 720P has an advantage for sports and fast moving action because it is 60 frames per second and is one of the reasons networks like ESPN, Fox, ABC chose to use this format. 1080i has better resolution but only 30 frames per second (60 fields ie odd/even lines) and is beneficial for non fast moving material. Now, which type of camera is used is a different issue
The native signal will usually look best if the display matches it as no scaling is invloved. Again this assumes all other factors are equal which they RARELY if ever are!
1080P/60 with 60 frames per second would be best! But, there is no one broadcasting 1080P/60! You can get 1080P/60 on blu-ray but most movies are 1080P/24 since film use 24 frames per second. Film rarely has fast motion. By motion I don't mean action but fast camera pans, films usually have cameras mounted on tracks or other devices that follow the action scenes and don't just pan the camera.
Hope this helps