When I installed Kubuntu, I used the alternate installer so I could encrypted the disk, and I ended up encrypting it with AES. However, I now regret that and want to use Serpent instead (it's a lot stronger if I'm right, and I can be really paranoid about computer security). So is there a way to re-encrypt the disk or somehow change the encryption method from AES to Serpent without re-installing?
Also, I know Serpent is stronger than AES but AES is faster, but how big are the differences? I want to change from AES to Serpent because I know AES is susceptible to a timing attack (and is weaker in general), but my TrueCrypt benchmarks place the speed differences far apart. I get 2.6 GB/s with AES and 241 MB/s with Serpent, according to TrueCrypt (encrypting and decrypting 1 GB of random data in RAM). Is the difference really that big in practice? If I encrypt my computer with Serpent would the disk really be more than 10 times slower?