Radeon x800 pro here, both 16 & 32bit modes give the same results, apart from GraphicsDepth() of course :)
Color red bits: 8
Color green bits: 8
Color blue bits: 8
Color alpha bits: 8
Depth bits: 24
Stencil bits: 8
Accum red bits: 16
Accum green bits: 16
Accum blue bits: 16
Accum alpha bits: 16
Double buffering supported?: 1
Stereo left/right buffers supported?: 0
Auxiliary buffers available?: 2
Maximum pixel-remap table size: 65536
Maximum texture size: 2048x2048
GraphicsWidth(): 640
GraphicsHeight(): 480
GraphicsDepth(): 16
GraphicsHertz(): 60
Color red bits: 8
Color green bits: 8
Color blue bits: 8
Color alpha bits: 8
Depth bits: 24
Stencil bits: 8
Accum red bits: 16
Accum green bits: 16
Accum blue bits: 16
Accum alpha bits: 16
Double buffering supported?: 1
Stereo left/right buffers supported?: 0
Auxiliary buffers available?: 2
Maximum pixel-remap table size: 65536
Maximum texture size: 2048x2048
GraphicsWidth(): 640
GraphicsHeight(): 480
GraphicsDepth(): 16
GraphicsHertz(): 60