I saw that no one mentioned the log buffer...

the log buffer clears every commit (independent of who issued it), or after 3 seconds, or when it becomes 1/3 full.

The log buffer should be able to hold 30% of the average transaction in the database times the number of concurrent active sessions. Most companies I have looked at very from 16MB to 128MB... you should really not go much more than this.

To decrease the speed of the log switches increase the size of the redo logs. You can do this be creating new ones, and dropping the old ones. You should also alternate devices on which the redo logs are stored. This will reduce contention while the database is creating the archive log. For example

Log1 is on /db01
Log2 is on /db02
Log3 is on /db01
Log4 is on /db02

and they should also be seperated from your datafiles and the archive log destination directory.

If you are still experiencing performance issues then perhaps you should look at the stripe size (or remove stripping entirely from that device) of the devices and increase it. The log writes in serial, and does not take advantage of the random access performance gain in striping.