Your system should be just fine to run 5 game clients (with ISBoxer) wherever you go assuming you're not
trying to run High or Ultra settings or with Multisampling enabled on more than just 1 client.

Just to elaborate on what Ualaa said, PB runs slave game clients at a lower resolution which saves on
computer resources, however, you don't get instant swapping. If you'd like the same "low resolution"
behavior in ISBoxer you would need to go into your Window Layout and uncheck the Instant Swapping
feature (which I don't recommend since it takes away from one of the many things ISBoxer is known for).
Instead, I would recommend using a Window Swapping Macro and details on that can be found here
(different than Ualaa's link although related).

Also as stated already, 30 background FPS can be slightly rough on some systems depending on what's
going on. Even with my higher end system I don't always run 30FPS background depending on what's
going on.