Assembly language to reduce encryption overhead

[MetalF]

Hi.
I'm aware that assembly language can be used to improve encryption performance, as claimed by DiskCryptor (another disk encryption app for Windows, but less user-friendly).
TrueCrypt did use assembly language too.
The encryption overhead is always there; also I know you lose the performance gain of Direct Memory Access (DMA) - I think it's because the data has to be decrypted by the CPU instead of being copied directly from the disk to RAM?
Would assembly code help speed things up? Could assembly also make it quicker to encrypt large drives?