Tuning NIC Performance?

With the advent of higher and higher broadband speeds to the small
business premise, I am finally seeing the limits of what some of the
older NICs could do.

I recently solved a throughput problem on a FreeBSD NATing firewall/gateway
by replacing the onboard RealTek connection with a PCie-based Intel 1G NIC.

Is there a resource somewhere that speaks to how I can further tune these 1G
NICs for best throughput?

TIA