Current Behavior: The GUI art for full screen 1920x1200 takes up a larger proportion of the screen area than the interface rendered in full screen 1280x1024, and is not scaled correctly. Using portrait area (L x H) as a metric for determining interface element size, portraits in the 1920x1200 screen are 150% larger by area than the 1280x1024 portraits, despite 1920x1200 having only 76% more area than 1280x1024.
It is possible the wrong chat log, portrait bar and option bar interface elements are being used, as the 1920x1200 interface lacks crispness and appears to be made of lower DPI art assets than the 1280x1024 interface. This imbalanced proportion of gameplay screen to interface elements can be seen clearly when comparing two images. The first image is full screen 1280x1024 (desktop res), while the second is full screen 1920x1200 (desktop res).
Note the proportion of the entire screen occupied by all interface elements at 1280x1024:
Compared the above image to how much of the screen is occupied by the interface at 1920x1200:
Expected Behavior: The GUI art scales with resolution, so that the proportion of the screen covered by the chat log, portrait bar and options bar is not greater at higher resolutions. Currently, improper scaling negates any benefit of playing at a higher resolution and is actually detrimental due to the lack of interface art fidelity and decreased viewable gameplay area.
Details: 1920 x 1200 is 76% more screen area than 1280x1024, as such one would expect all interface elements to increase in size by 76%, such that the total screen area occupied by the interface remains the same. I believe the root of the problem is the differing aspect ratios (4:3 vs. 16:10) and that the interface is being sized based on the difference in screen WIDTH (1.5x) rather than area.