It would seem that SF-2581 is the enterprise version of the consumer version SF-2281 (mentioned in the Hardware Canucks review, and speculated already here:
ADATA Shows Off Enterprise SSDs, RAM, NAND, etc.). Intel SSD 520 and OCZ Vertex 3 use this consumer version (SF-2281) Sandforce controller. The only difference seem to be that the SF-2581 comes with support for super capacitors to protect data in flight.
Check out the Storage Review test of the Intel SSD 520 with 20% over-provisioning:
Intel SSD 520 Enterprise Review | StorageReview.com - Storage Reviews
Their tests show both Intel SSD 520 and OCZ Vertex 3, using the SF-2281 controller, retain decent speed in steady state tests with 20% over-provisioning.
Doing the same manual over-provisioning with Kingston E50 I would expect to yield similar performance retention. Of course then you're looking at a 400 GB drive instead of 480 GB.
Doesn't sound too bad, considering the 3 DWPD endurance rating.