The performance drop is present on the Vertex 4 128GB, not sure if other capacities are affected (I read not). The Agility 2 is Sandforce based, this issue is unrelated to those controllers as far as I know.
Is this an issue on the 256GB model too? I read somewhere (don't remeber exactly where) that this issue was only present on the lower capacities. The 256GB SKU does not suffer such a severe performance degradation. Am I correct?