An important note is more important than frequency is your share rate -- which is more important than hash rate.
Share rates depending on difficulty and pool settings and can be different for the same coin depending on where you are mining. This makes the share rate a poor metric except for comparing machines connected to an identical pool.
Share rate is what you get paid on. And yes, it varies by luck and such... within a pool, share rate is how I'd measure the effectiveness of a modification... so I stand by my statement.
Jason