My intended final build price is around or over $1500 (trying to get a "futureproof" computer, as hard as that is. Have a lot of stuff from earlier, like keyboard/case/mouse, so I can spend some more money getting higher-end).
1) I would avoid an Open Box component. It was returned for some reason or another so why risk it?
2) I lean toward the ASUS, as I favor them over Gigabyte. However, Gigabyte is the best valued overall LGA 1366 board. It is truly a tough decision but based on your cost concerns, I recommend the Gigabyte.