I think most people like science, so most forums I think will be applicable. I think if I narrow it down to just science it might cut out a lot of potentially interested users.
cool! you might want to include a restriction on forum topic, so that it relates to science at least.
Even newcomers with a science background complain they don't see whether their setup is configured correctly.
Gridcoin as of now is a still a topic for geeks and setting up BOINC is complex and might end frustrating.
Without restriction, your promotion could end up in a forum of pet lovers between guides for Chihuahua nutrition.