is there a guide anywhere that explains what the video setting do?

[bugmenot]

There is, google each and every foreign term, it's there on opengl documentation.

but honestly,

So, to the different options:
- Disable VBO:
using OpenGL VBO (http://www.opengl.org/wiki/Vertex_Buffer_Object) should always
bring a win. This option is probably useless.
- Only GE graphics:
the PSP allows drawing using GE commands or by writing directly to the PSP
framebuffer memory. With OpenGL, supporting both methods is cost expensive.
When this option is activated, only the drawing using GE commands is supported.
If the application writes directly to the PSP framebuffer memory, this is ignored.
As a side effect, a more accurate FPS is displayed when enabling this option.
When disabled, the displayed FPS is over-optimistic. This is why a lower FPS but
a smoother/faster play is often reported. Trust the faster play, not the FPS ;-).
- Use Vertex Cache:
when enabled, parts of the graphics (positions, colors, bones...) are loaded on
the graphic card and reused from frame to frame when their data is not changing.
This has however a negative impact if the game programmers are changing their data
(e.g. the positions) very often.
By the way, a texture cache is always used and cannot be disabled.
- Use shaders:
use vertex and fragment shaders to implement most of the PSP functions. Some of
the PSP functions cannot be implemented without the use of shaders, so this option
should provide the most accurate rendering. Unfortunately, some shader
implementations are somewhat buggy, depending on the graphic card used
(e.g. AMD/ATI or Intel).
- Use a Geometry shader for 2D rendering:
when using shaders, this option might bring a slight performance improvement for 2D
applications.
- Disable UBO:
when using shaders, OpenGL UBO's (http://www.opengl.org/wiki/Uniform_Buffer_Object)
should bring a better performance. But again, some graphic card drivers have
sometimes buggy implementations. This is why this option is enabled by default,
and only a "Disable" option is available.
- Enable VAO:
an OpenGL optimization (http://www.opengl.org/wiki/Vertex_Array_Object) when
similar graphics are grouped together. This is just available as an option as most
PSP programmers do not following this approach.
- Enable saving GE screen to Textures:
the content of the PSP framebuffer is kept in an OpenGL texture instead of the PSP
memory: This allows faster load/save from OpenGL, but breaks compatibility if the
application is manipulating directly the framebuffer memory.
- Enable decoding of indexed textures (using CLUT) in shader:
this option brings a performance boost when combined with
"Enable saving GE screen to Textures" and when the application is doing
manipulations on the Red/Green/Blue color channels of the framebuffer
(e.g. to implement some graphic effects, blurs or shadows). Available only as an
option as it might break the compatibility for other applications...
- Enable dynamic shader generation:
we have a single shader implementing all the PSP functions. This shader contains
of lot of condition tests ("if (mode==0) then xxx", "if (mode==1) then yyy") to
support all the combinations. This option enables the generation of a separate
shader for each combination. E.g., when mode==0, we create one shader containing
only "xxx" and when mode==1, we create another shader containing only "yyy".
Each of these shaders will then execute faster because it can avoid the condition
test. Due to the large number of possible combinations, this could result in the
generation of several hundred different shaders. As this might overload the graphic
card driver, this feature is only available as an option. As a side effect, some
graphic card drivers (e.g. AMD/ATI) are reported to be less buggy when using this
option.
- Enable the shader implementation for the "Stencil Test":
the PSP supports a "stencil" function used to implement some graphical effects.
This function cannot be implemented correctly using the standard OpenGL functions.
When enabling this option, an implementation matching the PSP features is
activated through the shaders. The option is only relevant when using the shaders
and is only available as an option because it has a negative impact on the
performance (lower FPS).
If your application is not displaying correctly or is logging the warning
"Both different SFIX (NNNNNNNN) and DFIX (NNNNNNNN) are not supported"
you might try this option.
- Enable the shader implementation for the "Color Mask":
if your application is logging the warning
"Unimplemented Red/Green/Blue mask 0xNN"
you might try this option. It might increase the quality of the rendered graphics,
but is only relevant when using shaders.
It is only available as an option because it has a negative impact on the
performance (lower FPS).
- Disable optmized VertexInfo reading:
you might try this option if graphics are sometimes corrupted.
This option has a negative impact on the performance (lower FPS), but
provides higher compatibility.
- Use Software Rendering:
this option enables the emulation of all the PSP graphics in software by the emulator.
The hardware of your graphics card is not used (well, it will just be used
at the very end of the rendering to show the rendered image).
The software rendering is much slower than the hardware-based rendering using
a modern graphics card (GPU). But it allows a much higher degree of compatibility
and avoids rendering problems related to buggy OpenGL drivers.

Those looks pretty darn good and fairly noob friendly writing to me. If you need to understand each and every sentence out of that, then you'll need to go in-depth on graphic programming, which may require a Diploma course to finish.