Agreed you won't need much to max out a 100 Mbps connection.

I have a few relays in the ~ 200 Mbps ballpark running on single core VPS instances. The underlying hardware is based on Intel Xeon E5-2650L.

CPUs with AES-NI help. 2 cores may offer marginal improvement. More than 2 cores isn't going to help at all. Tor still isn't optimized for it.

If running on Linux or Unix there are a lot of optimizations to be done. For Linux, I'd start here: https://www.torservers.net/wiki/setup/server and look at the "High Bandwidth Tweaks" section.