With your existing system I doubt you would be able to play any of the recent games at full effects, if you use the same games as you do now then they would fairly fly and may not notice any performance hit.
Terminate is different to stop on-access protection, as you are only stopping a single provider, terminate can be temporary or permanent (if you select Yes to the persist the changes question). During which no scanning will take place for that provider.
The Stop On-Access Protection no scanning for any provider takes place and you need to Start On-Access Protection when done with the task. The services wil still be in a running state but no scans otherwise you would need to reboot to restart them.