There are a few factors to consider here.
- In general, home encryption does not have noticible performance impact.
I use AES encrypted home on Natty running off a Persistent USB install
To help firefox, I run its profile off a tmpfs ramdisk.
At this point, one question will be, how much security do you want?
My intention is to just secure my Persistent USB data in case the flash is lost.
- While you have lots of data in your hoem, do you really access all of it during a session?
If not, this should not matter -- the filesystem is not decrypted completely; only data being accessed is decrypted.
- What is your system configuration?
Specifically your processor power, system RAM and disk performance.
If these are moderate or more you are not likely to see an overhead.