Very likely it will be just fine.
Another way of looking at it: what's the CPU load on your I7 Win client?
Not exactly an apples-apples comparison, but I'd be surprised if you see an appreciable CPU load @90Mbit/s.
The main thing that would slow down pfSense would be the introduction of a resource hungry package like Snort/Suricata.
With a reasonable amount of memory (1GB would be a start) and the CPU you mentioned, that system should be entirely adequate for VPN across 100Mbit cable.
You might want to check with your VPN provider if they have any particular configuration issues w/pfSense (or perhaps search the other pfSense boards).