Finer grain GG will make the illumination more uniform
and is easier to focus on but won't make the image much
brighter. Before investing in the glass try washing the
glass you have. If the ground side gets a bit greasey it
will become a bit more transparent causing it to have a hot
spot and look grainy. Dishwashing detergent in warm water
will work fine.
  I am not familiar with Satin Snow. There are three ways
of making ground glass. One is to sand blast the surface,
this yields the coarsest surface, the next finest is
grinding it with rouge, the third method is acid etching.
The last gives the finest surface. That may be what this
outfit is doing.
  I used to get very satisfactory GG from Edmund Scientific
but it was no longer in the catalogue after the company
split into two. I think Edmund Optical may still have it.
  A tip, ground glass is best cut using a carbide scribe.
The familiar wheel type window glass cutters will cut it but
not very accurately. You can get a scribe from a hardware
store for less than $10 US.