MaximumPC executou alguns testes:
However, when we busted out the hard-drive-intensive benches, we immediately saw as much as a 20 percent hit on the encrypted system. We're not sure the PCMark06 slowdown represents real-world performance, but our Photoshop script, which includes tons of hard-drive-intensive reverts, showed a 10 percent hit as well.
What's the bottom line? We're not going to enable BitLocker on systems that don't hold crucial, mission-critical data.
Benchmark (unidade não criptografada; unidade criptografada):
FEAR (FPS); 56; 57
3dMark06; 8071; 8082
PCMark06 Hard Drive Suite; 6133; 4948
Photoshop CS Script (Sec); 303; 330
Claro, rodar benchmarks 3D realmente não faz sentido, já que você dificilmente vai criptografar uma plataforma de jogos, mas no final é um trade-off simples: performance para segurança.