Advice on encryption of external disk

[Celejar <celejar@gmail.com>]

Hi,

I am preparing a USB external HDD for use with my T61 ThinkPad (Core 2
Duo CPU T7300 @ 2.00GHz). The disk will fulfill two, very different
functions: general backup for files (mail, documents, etc.) via
rsnapshot (rsync type backup), and overflow storage for my full main
HDD ("big" files such as media: audio, video, PDFs).

For the backups, I need encryption; the media storage doesn't require
it. Currently, I use different partitions on my external disks: plain
for storage, and encrypted (dmcrypt / LUKS) for the backups (and
storage of sensitive information). This obviously adds complexity, so
I'm thinking of going to one encrypted partition for everything. The
obvious possible downside is performance: everything I read indicates
that there is a significant hit, even on modern hardware, but I don't
really know if it's current, accurate, or relevant to my use case.

What would the experts recommend: one partition for everything for
simplicity, or separate ones for a possible performance advantage?

Celejar