Encryption vs performance

Question

As a laptop user I have always felt attracted by the use of encryption but as the laptop I am using is quite old (T23 - 1.13 Ghz / 256 RAM) I wonder if the gain of security would come at a too high price in terms of performance.
Someone has used or is using encryption for a similar (or old in general) laptop and can share his/her experience in terms of gain/loss?
Thanks in advance for any input.

Answer 1

@fledermann
No worries. Thanks anyway for the info.
@Strike0
I totally forgot about that. A kernel update came along and I thought 'Well, will reply after rebooting and paste it' but as usual new things started crossing my mind afterwards and in the end I did not include the results in my reply.
The results are as follows:
# Tests are approximate using memory only (no storage IO).
PBKDF2-sha1 51522 iterations per second
PBKDF2-sha256 46545 iterations per second
PBKDF2-sha512 17210 iterations per second
PBKDF2-ripemd160 75851 iterations per second
PBKDF2-whirlpool 22080 iterations per second
# Algorithm | Key | Encryption | Decryption
aes-cbc 128b 21,6 MiB/s 30,7 MiB/s
serpent-cbc 128b 12,8 MiB/s 16,5 MiB/s
twofish-cbc 128b 36,1 MiB/s 38,1 MiB/s
aes-cbc 256b 23,5 MiB/s 23,7 MiB/s
serpent-cbc 256b 12,9 MiB/s 16,5 MiB/s
twofish-cbc 256b 36,0 MiB/s 38,2 MiB/s
aes-xts 256b 30,7 MiB/s 29,8 MiB/s
serpent-xts 256b 12,9 MiB/s 16,4 MiB/s
twofish-xts 256b 37,4 MiB/s 37,0 MiB/s
aes-xts 512b 23,7 MiB/s 23,3 MiB/s
serpent-xts 512b 13,0 MiB/s 16,3 MiB/s
twofish-xts 512b 37,1 MiB/s 37,0 MiB/s
As for ewaller's example I understood it both as an simple example of a possible encryption scheme and as the suggestion of using more than one security 'layer' depending on the needs. Taking into account your comment I presume I should disregard the example and focus more on the suggestion.
Regarding the access of 'other legitimate users' I didn't mean to refer specifically to a spouse, partner etc. which I consider to be part of a trustworthy circle but to 3rd persons that ocassionally may use the equipment. Like a guest who wants to check his mail or the tech support in case something is wrong with the computer. Especially in the later case I have personal 1st hand experience of the technicians being at the same time (or even more) interested in going through the user's personal data (the client was a girl) and fixing the problem the computer had.
Taking this into account you will understand that I don't consider myself the provider of any content for this or similar kind of people even if it the most harmless one can think of (still private in the end though).
The size of the 'private container' is indeed a tricky thing, just like it is when thinking of how to setup the different partitions when installing a Linux distro.
The size drcouzelis suggested looks fine to me, even, to some extent, excessive but I presume it is better to overestimate than to underestimate.
As for 'excluding' the home partition from a general disk encryption setup, well, as long as it works as it should I wouldn't mind trying that out but as you yourself state it indeed sounds trickier to setup. Thus I would be tempted to first try out the secure directory setup as explained in the wiki. But I understand, at least I think I do, the idea of your suggestion. Once I go through the documentation available I will most likely end up more or less convinced.
Just as with regards to a specific/'personalized' encryption for the home partition in terms of using a different filesystem I wonder if it wouldn't come to the considerations of using X filesystem for X type of files just as one does when choosing the filesystem for the partitions. I mean filesystem A might show better performance because the encrypted files are of type B which it handels best.
Therefore wouldn't I end up being a 'hostage' of those type of files when the data to be encrypted would be of 'mixed nature' (larger, lighter etc.)?