@JKnott:
I'd expect you'd have trouble finding a computer that could keep up with 100 Gb. High bandwidth network gear generally uses a lot of custom hardware to handle the processing.
PCI Express lanes are the real problem requiring X16, we have found a motherboard/cpu combo that has no problem pushing 100gbps. SuperMicro X10SRi-F Motherboard with a Intel Xeon E5-1630v3 is capable of doing so. So don't be afraid to try different things, this is the current configuration for our 100G test nodes. We currently have Mellanox, Broadcomm, and QLogic NICs in the field. Though the Mellanox has proven to be the more stable card at the moment (bleeding edge can be interesting at times).
@ivor:
Current pfSense architecture will be the biggest limitation in achieving such speeds. We have demoed next gen "3.0" which is capable of doing 40Gbps IPsec, so far. We intend to demonstrate 100Gbps IPsec in the following months.
Here's the talk on it by our Jim Thompson https://twitter.com/NetgateUSA/status/923994053015982080
Thank you, I'll give that a look. We are jumping from 10g to 100g and skipping 40g (probably)