[XPERIA X8 General] epithetic:
To reiterate and expand on my post here:

SD card:

Do NOT make an ext4 partition with swap (and make sure there isn't one)

System setup:

Flash minicm9 and gapps as normal

Remove unwanted applications and services (e.g. for me, Google Talk, FM radio, etc.).

Remove DSP Manager.

If you like the dark ICS theme, you can replace your Contacts.apk, Mms.apk and Email.apk with the ones from here. Flashing doesn't work for me, but you can extract and copy them manually. Do not replace your music.apk.

Flash this zip to get SRS audio support if you want virtual surround when listening to music on earphones (stock player). Similar to what the DSP Manager can do for you, but a lot more lightweight.

Do not

'install a2sd' via console

System configuration:

Set up your autobrightness settings like this

Test your pulse notification light. If it stops flashing after a couple of seconds, go to system/lib/hw via your root file manager and delete/rename lights.shakira.so. Once you reboot, your notification light should work normally.

Disable Google's location service (GPS is okay)

Min CPU: 320MHz (important); Max CPU: ~? (I use 748)

Governor: SMARTASSV2

Disable zRam

Do not enable 'Allow purging of assets'

Do not enable Kernel samepage merging

Surface dithering: Yes

16bit transparency: No|Yes (up to you)

You should now:

Have a for the most part very fluid minicm9 (using Trebuchet). There should be no crashes or instablity, apps will not hang or FC. Memory will feel a little short, but apps should load quickly enough and be incredibly responsive once loaded. Stock browser will choke on low memory, I suggest Opera mobile as an alternative.

This is a very usable state of affairs, but if you want more and have a decent SD card, keep reading:

Performance tweaks:

Do NOT

use Supercharger.

Move large apps that are not usually running to SD (e.g. Opera) via Settings»Apps»Move to SD. If this option is greyed out, follow this guide to move them anyway (NB: the command for the ICS platform is set-install-location rather than setInstallLocation).

Install SD-Booster and a SD card speed test of your choice. Adjust the cache until you get an optimal read/write speed (for me, this is at 4096KB) – more is not always better. You can uninstall the speed tester once you're done.

Install Swapper2.

Set swap place to somewhere safe on your SD card (do not use an ext partition)

Set swap size to at least 128M, I recommend 256M.

Set swappiness to 20

Advanced options» tick Recreate swap file and Reformat swap

Enable swap once (may take a bit as it writes the file).

When it says 'Done' open Terminal emulator and type in 'free'. You should now see the available swap (however much you set).

Go to your favourite file explorer and navigate to your swap file/folder. Make a copy of the .swp file

Back in swapper2 go to Advanced options again, and UNtick Recreate swap file & Reformat swap. Once you hit okay, it should say 'Swap file removed, all ok!'. Note that enabling swap will now fail as it can't find the file (bug?)

This is why we made the copy back in your file manager. Open it up and rename the copied swap file to its original filename.

Back in swapper2 (without touching the settings) click 'On'. It should now enable swap just fine. Verify in terminal, and you are done!

Note that to connect your USB storage, you will have to turn off swapper2. As you don't recreate/format swap every time this should be pretty much instantaneous (as long as you remember to do it!)

Your ROM should now still be running every bit as smooth as it was before, BUT you should have a lot more memory to work with, which means apps will no longer reload all the time (I would still suggest to free up apps via home button » swipe if you no longer need them).

Enjoy!

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If you've set everything up properly, this should be about what you can expect in performance:

http://vimeo.com/42602916

(pass to view is xda)