I have mine running on adaptive with a 1Gig fiber connection and multiple vlans. Never noticed any issues. I have multiple servers running behind the firewall as well. Some for outside things like games and teamspeak. The CPU is an E3-1231 V3. Been running for a few years and never had an issue as described. Not sure why it would effect anyhting. It's not like the CPU gets much actual load unless you are doing a lot of scanning/inspecting of packets.
Do you have any more details on what seems to cause these issues in relation to the power settings? Maybe some decent writeups?