OSX: Getting an accurate list of supported screen resolutions in CaptureDisplay mode?

For my cross-platform 2d computer game, I’ve been trying to determine how to best handle multiple resolutions with an in-game menu in Unity.

In order to support retina screens in OS X, I discovered that I need to set
Mac Fullscreen Mode to CaptureDisplay in the player settings. When I do that, Screen.Resolutions reports

640x480
720x450
800x600
840x525
1024x640
1024x768
1280x800
1440x900
1680x1050
1920x1200
2048x1280
2560x1600
2880x1800

However, when trying to set the screen to some of these resolutions (for example, 720x450), I got an error in the dev console: "Could not find requested mode."

On the other hand, in FullscreenWindow mode, the listed resolutions are

640x480
720x450
800x600
840x525
1024x640
1024x768
1280x800
1440x900
1680x1050

I can switch to all of these resolutions, but doing so stretches the screen contents to cover the entire display rather than supporting the chosen aspect ratio with black bars like in CaptureDisplay mode, so CaptureDisplay mode seems to be a better choice than FullscreenWindow mode overall (after hacking it so that command-tab switches to windowed mode rather than blocking input).

My question: how can I get an accurate listing of available resolutions in Capture Display mode on OSX (I’m using a late 2013 Retina 15 inch Macbook pro running OS X 10.9.3, but I obviously want my game to run properly on every machine possible)?

Alternatively, what is the best way, from a user experience standpoint, to user-selectable resolutions, ideally with the ability to select the maximum resolution available - 2880x1800 in this case?
Do I need to write a native plugin to do this?

Retina is a scaled desktop. a 720x450 HiDPI (Retina) is actually a 1140x900 display. When you directly the capture display, 1440x900 is the screen resolution.

If you run at 720x450 in a FullscreenWindow on Retina the game is only 720x450 with pixel doubling in both horizontal and vertical. Just run the game at 1440x900.