Ooh, Sammy R88
AFAIK, the R8 range is the successor to the R7 range (I've got a 26" R73). Main difference, I think, is that the R8s have 2 or 3 HDMI sockets, compared to the single HDMI I have on my R7.
Definitely has the same native resolution as the R7s - 1366x768 pixels.
If using component to connect the 360, the closest optimum res. would be 720p.
If using VGA, the closest optimum res. would be 1360*768.
I'd still go with 720p, rather than 1080i, as 360 games are at 720p & the TV itself is best at 720p.
But it's all down to personal preference... some people think 720p looks better, others think 1080i looks better. Try both & see