I finally decided to test FSX with Supersample antialising and I'm quite impressed. I think it speaks for its self, but it takes a lot of power to run it..
Not only does it remove virtually all aliasing, it really sharpens up the image. Most noticeably the writing and red lines.
These images are 1:1 crops of the aircraft preview window at 1600x1200, using 4x Supersampling, regular 16x AA, and 2x Supersampling. Even 2xSS looks better in ways yet gives good performance. The second set is 4xSS and 16xAA at 1.25x.