The Sandforce drives can have their write speeds slow down after heavy use, and even TRIM does not recover the performance. If you look at their forums, lots of people have seen this, and OCZ has claimed that this is a feature, and that the performance will recover in about a week. It does not sound like a feature to me. I suspect Sandforce did not intend for the drives to behave that way. Regardless, unless Sandforce documents under what conditions this can happen, and for how long the performance drop occurs, then the behavior is undocumented and it is certainly a bug. But it has been known for a while, and Sandforce has not yet fixed the bug or documented the "feature".