Tem,

   I've never heard anything to the effect that the signing causes types in
the assembly to run slower.  Granted, there might be a one-time hit for
verification, but I can't imagine it is that substantial.

   Of course, you can always run some performance tests for your signed and
unsigned assemblies.

   In the end though, I think you will find little, if any difference.
Also, signing is still a good idea because it prevents the assembly from
being modified in a way that would allow it to continue to run (since the
hashes wont match anymore).

   This means that you have to make sure that the key used to sign the file
is secure.