In practice, SandForce based drives running a mainstream client workload do very well and typically boast low average write amplification. However if subjected to a workload composed entirely of incompressible writes (e.g. tons of compressed images, videos and music) you can back the controller into a corner.
To simulate this I filled the drive with incompressible data, ran a 4KB (100% LBA space, QD32) random write test with incompressible data for an hour and a half, and then ran AS-SSD (another incompressible data test) to see how low performance could get:
I usually run this test for only 20 minutes but after seeing an unusually resilient performance by the 240GB drives I decided to extend the test period to a full 90 minutes. Performance does drop pretty far at that point, down to 103MB/s. TRIMing the drive does restore some performance but not all. If you have a workload that uses a lot of incompressible data (e.g. JPGs, H.264 videos, software encrypted data, highly random datasets etc...) then SandForce just isn't for you