Thanks eleuthria. I'm interested in the method you use to calculate the SPM target and how it's affected by difficulty changes - is the algorithm posted somewhere?
The full SPM is based on a 5 minute average. If they are 20 SPM or higher, the difficulty is doubled. There are extra adjustments during shorter time intervals to catch extremely fast miners in under 5 minutes. Additionally the difficulty is halved if no shares are submitted after a minute, or if SPM drops to 6 or less (which would only happen if the miner leaves the server/turns off miners behind a proxy).