It's not quite that simple unfortunately. Just looked up your TV's specs and, as I suspected, the actual resolution of the TV is 1366 x 768. So feeding the TV 720p means the TV is actually having to upscale it to fit the 768 horizontal lines. On the other hand, feed it 1080p, it will have to downscale it to the 768 lines.
I think in the vast majority of circumstances, you're not going to see any difference between the two, but, I have noticed previously that GT Prologue did look slightly better at full speed round some corners when using 1080p compared to 720p (my TV has the same resolution). How close you sit will be a bearing though, as mine is a 42" so is easier to spot things like this.
Try them both - if you prefer one over the other, use that one. If you can't see the difference, then it doesn't matter!