I found some additional information the in LCD driver page: http://processors.wiki.ti.com/index.php/AM335x_LCD_Controller_Driver's_Guide
Looks like my mode is 800x480-62:
root@am335x-evm:/home# fbset
mode "800x480-62"
# D: 30.000 MHz, H: 32.433 kHz, V: 61.895 Hz
geometry 800 480 800 960 32
timings 33333 39 39 29 13 47 2
rgba 8/16,8/8,8/0,8/24
endmode
I tried setting a striped 800x480 to the display just to see what it would do:
$cat my_logo.bmp > /dev/fb0
and it appeared on the display... but it show up 4 times overlapping itself slightly (shifted so I can see 4 images "stamped" across the display)