1360x768 is the best you're going to get.
1080i. 'i' draws half the screen every refresh, odd lines then even lines, back and forth. Thats why catalyst control center only shows 30 hz, because thats how often the whole screen is being refreshed. Another drawback of 'i'nterlace is that you will experience screen tearing because every other line isn't synced.
1080i is ok for movies without much action, but when being used for computer screen its best to use progressive scan, in this case 720p, and with overscan 1360x768.