Look at stats on the database
(need timed_statistics = TRUE for meaningful stats)
A raw figure will be
redo write time / redo writes = avg. redo write time
This will be in writes/ 10s of millisec
The quickest log switch interval is something different
there is a script on http://www.ixora.com.au called
log_switch_interval.sql to determine this.
I suppose some extrapolation could be used to determine the average log switch interval
i.e redo size / redo write time = avg redo write speed
in bytes/10s of millisec
Then the average time will be the
redo log size / avg redo write speed
Performance... Push the envelope!