Yes I had the same problem, CCC AA worked at 720p but not 1366x768.
Did some digging around the old interwebs and discovered that this is not a unique problem, it has to do with the available standard resolutions at the time UE3 was in development for PC (the 360 version doesn't care it runs at 720p and that's all) and at this time 1366x768 was not a common resolution but 720p, 1080p etc were (1680x1050 seems to be similarly broken along with many other 16x10 variants).
There is apparently a registry hack that can help (although it's been done to enable 1680x1050 but you might be able to change it to 1366x768) here http://forums.guru3d.com/showthread.php?t=359712.
Alternatively as I said setting the AA profile in Radeon Pro to Unreal Engine 3 and forcing it that way works just fine (at least it did for me with an HD7850 with 14.6 betas and the latest build of Radeon Pro) although I still much prefer to use SMAA due to it's lack of performance hit and better edge smoothing than MSAA often manages (SSAA is just overkill at 1366x768 anyway there's simply not enough on screen pixels for it to add enough blended ones to edges to hide all the jaggies and the performance hit for most console ports makes it pointless, works great with older games though especially IDTech 3 era).
Personally If I had the rig you have I'd invest in at least a 1080p monitor rather than sticking to the 1366x768 ones we both seem to be using, after all what's the use of all that pixel pushing power if you don't use it?