Remember, SandForce’s technology only works on files that are easily compressed. Good encryption should make every location on your drive look like a random mess, which wreaks havoc on SandForce’s technology. With FileVault enabled, all transfers look incompressible - even those small file writes that I mentioned are usually quite compressible earlier.
The improvement in storage performance is even more revolutionary. Similar to the rMBP, with the 2012 MacBook Air Apple has entered the world of modern SSD performance. The impact of the faster SSDs is felt everywhere from boot to application performance. Once again there are two SSD suppliers, but unlike in previous models both can be deliver good performance. If you use FileVault or plan on working with a ton of already compressed data, you’ll want to pick a 256GB or 512GB drive to end up with Samsung’s controller rather than the SandForce driven Toshiba solution.