I own the vx-2, a 720 dlp 3 chip.
there are significant differences between the 3 chip and the 1 chip even with runco.
As you know there are differences between 720 and 1080 but it becomes abundantly clear when the screen is over 80 inches or there is alot light in the room that a 1080 better helps with the details
While 720 is excellent, you may want newer technology. They have 720 on the vivxII processor. I use component to for my sound which produces excellent results. Use a good quality DVI cable if you go this direction. Synergistic research makes a very good one (keep length under 25 ft.
One final thing - vidikron vs runco. If you align the models based on specification you get yourself in the ballpark of which. Price is the same once you spec.
Consider two other things:
1) If you buy used, buy form a dealer who has provided a project lamp free and new
2) Buy the extended warranty, it is worth it
Make sure it has recently been factory serviced so you have the latest software loads.
Hope this helps.