The logs from frags don't seem to affect the cpu very much. There is a lot more log spam when there are issues like no playerstarts available, or accessed none errors. Even with that excessive spam it doesn't seem to bother the cpu very much.
Some years ago, something caused enough spam in my server log to make the log file size too large between checks, by the ucc.init script from ASU, that it automatically restarted the server believing the server was stuck in a loop but it was so long ago now I can't remember what caused it. Whatever it was, map or mod, I must have just removed it from the server. There is an option in ucc.init to increase the MaxLogFileSize but mine is still set at the default of 1024.
The biggest issue, besides lots of players, for the cpu seems to be maps with lots of moving items. I had to remove both ctf-foosball and ctf-toywars because they ran the cpu too high with a full server.
