I'll answer these from what I understand here...
This sets the interval at which the zmmtaconfig process checks the postfix configuration files for changes and reloads them if there are any. This has been known to cause high CPU usage on some systems and is probably the only reason your CPU usage has dropped.
zmlocalconfig -e zmmtaconfig_interval=6000
This sets the maximum age for your log files, I'm not entierly sure what this would have to do with performance though as it just says when to delete the old log files. (7 days)
zmprov mcf zimbraLogRawLifetime 7d
Not entierly sure what this does as there is no "summary" log that I know of, but again from what I can find in the wiki this would only affect disk space usage, not CPU.
zmprov mcf zimbraLogSummaryLifetime 30d
From what I can see the only affect this would have is that it optimizes the logger tables when it runs, so it might have sped up access to them, thus slightly reducing CPU load on access to these tables.