I highly doubt that cutting the pyramid foam to place inside your case would work... That stuff works on the principle that it absorbs some noise but also redirects what it cant absorb thus dissipating the noise in the room. It would work better if you put the case inside a box lined with the foam (but then there's no airflow...). I'd go with the SilverStone stuff because it is much like the sound dampening stuff you'd find included in some cases (i.e. Define R5).
I use both I like the pyramid stuff I think it works much better just get some 3m spray glue and its go time, ThatBootsGuy is correct that the pyramid foam redirects noise so make sure you place it intelligently. That is place the foam so that it refracts onto other foam, thus deading the noise.
The Silverstone stuff is also a good product; it looks good it's easy to cut and install, it has its own adhesive backing, but it's not as dense as some of the other stuff nor as thick. What I will say for the Silverstone foam is that they give you your monies worth one pack really can cover a mid tower.
The problem with the Silverstone stuff is that it's expensive, and I want a cheap alternative, however if the Silverstone stuff was to work better, i'd go with that.
