How close to saturation can I run?
I work for a small college. Currently, we have a 45mb/45mb line coming into the campus. We have been using an Allot Netenforcer, which has allowed us to run at full saturation (at least of our downstream pipe) almost 24/7. Those groups and services that need priority get dynamically bumped up depending on time of day and how much bandwidth is being used by lower prioritized services.
We are considering switching away from the Allot when we increase our WAN connection, since going above 50MB will require both new hardware and a pretty hefty increase in licensing costs. If we went with pfSense, we were curious just how close we could run to saturation at our new bandwidth (probably either 100 or 200 mb).
The answer sadly is 'it depends'. DS3 lines (I'm taking a shot in the dark that is what you have) are pretty stable and have good SLAs. Assuming you are going to an ethernet private line or other service of similar caliber, you can likely run up to the high 90s percent wise (97-99) asuming you have a good /stable carrier.
The short answer is as long as your limits / QoS rules 'kick-in' before the carrier's your all set.