[citation][nom]omvo[/nom]I can set my 1080p monitor to 1600x900 on Desktop Properties in CCC. HD5870 and 10.9 drivers, I can also see 1600x900 as a selectable resolution in Starcraft II. I can send you screenies if you want.[/citation]
OK, so the original problem was with the notebooks, because those had 1920x1080 displays and I wanted to test at three native aspect-ratio resolutions. I have a bunch of
notebook charts here with ATI and Nvidia solutions, where the 1600x900 data is there for the Nvidia notebook but not the ATI. That's because the notebook didn't allow me to set 1600x900. So, I rechecked a desktop card:
Radeon supported 1600x900 on a 1080p display, just like you said. Thanks for pointing that out. The problem was that, because the "Extreme" profile in 3DMark requires at least a 1920x1200 display, I was using either a 1920x1200 or 2560x1600 display to test desktop graphics. The odd part is, Radeon supports 1920x1080 on the same16:10 displays, but not 1600x900. And it's not a fault of the monitors, because my GeForce drivers support 1600x900 on everything.
More information: If you look at Radeon and GeForce card options, using the same display, Radeons usually support a bunch of weird resolutions that GeForce does not, while GeForce supports a few resolutions that Radeon does not. But I was looking for 1600x900 specifically to find a 16:9 ratio to test that falls about half-way between 1280x720 and 1920x1080.
Making a long story short, in order to run the benchmarks in the preferred manner, ATI requires me to swap monitors while Nvidia does not.
Check
This Search Queue for more information on ATI's checkered past with 1600x900, to see how confusing this issue can be.