[Xperia Arc Q&A, Help & Troubleshooting] mhadjih:
KitKat 4.4.2 AOKP and ART-runtime enabled

It is very well possible to use KitKat 4.4.2 on our phones. Even with ART-runtime enabled. I personally use AOKP (Android Open Kang Project)'s KitKat version, and I managed to get ART-runtime enabled and running very fast and smooth.

You can find the ROM here: http://xdaforums.com/showthread.php?t=2624761

Of course you have to first install the kernel, which is given in the zip-file. Just unzip the kernel and Flashboot it to your device. Then go into CWM-recovery and go to Mounts and Storage and activate USB-mount. Locate the full AOKP-zip and place it on your SD-Card, as wel as the minimal Gapps for 4.4.2., found here : http://xdaforums.com/showthread.php?t=2012857. Unmount the USB, and install the zip as usual through the menu for it. Then, after installing AOKP, install the minimal Gapps.

Reboot and let your device sit for a while, or play around with it a bit....

I proceeded with installing Mounts2SD from playstore, while before having prepared my class10 8 Gb sdcard into two partitions. One partition FAT32, size about 6Gb and one partition EXT2 size around 2 Gb. Move everything to SD-card through the menu of Mounts2sd, except Dalvik-cache. NEVER MOVE THIS!!! (Don't move dalvik-cache to SD...)

Reboot at least two times to let the script (Mounts2sd) settle in... After this I installed Pimp-my-Rom from playstore and activated the nav-bar and some other scripts to improve the experience. Also I odexed (after finishing all my modifications) the phone through this : http://xdaforums.com/showthread.php?t=2527732

I then went to CWM-recovery through a reboot and made a full backup, which I advice you to do also, in case something goes horribly wrong.

Reboot to AOKP. As you can see, this ROM is awesome-fast beyond belief already. I had benchmarks in AnTuTu of around 6000, with NoFrills-CPU at 1401 Mhz. But, it can be faster if you choose to run ART-runtime instead of Dalvik. Be sure to remove all unwanted programs before switching to ART-runtime, because it'll take a lot of space in cache, and every program you don't need (system-programs that is) will reserve more space for ART.

Only and ONLY if your system is running smoothly on Dalvik, I advise you to go to your Phone-settings, (under Settings of course) and tap on 'Build-number' like 10 times. You will now become a developer. An extra menu will appear under Settings, where you can choose to run the ART-runtime library. Choose this and you will reboot.

Wait, wait and wait a long time for reboot. After initial booting everything has to be updated to ART-compiled apps. This will take a long time per app. Just wait and don't disturb your phone. If you get to the phone after booting, then you probably succeeded... You can check under the same settings-tab under Developer-options. If ART is selected, then you have it.

I strongly advice in case of mishaps regarding loss of network etc. to just reboot. Wait, wait and eventually you'll get there. Make a backup as soon as you have a stable working system under CWM-recovery.

I have been running stable ART under this AOKP-rom for about two weeks now and I'm really happy with it. Not only is the phone lightning-fast (6417 under AnTuTu, with CPU on my Arc LT15i on 1401 Mhz), but smooth as hell! Batterytime is amazing. This is as fast as it's gonna get! (I must have tried almost every ROM out there from stock 4.0.1 to 4.4.2...)

Hope you'll try and may it work for you too...!

(BTW my ultimate thanks to the guys from Open Kang Project!)

P.S. stock-browser is lagging... as usual under 4.4, but I use Dolphin and it is fast! Some toggles require reboot to function again. Some programs might fail you due to not being ready for ART. Facebook is a mess for instance, sometimes quitting unresponsice etc. Otherwise I have encountered no problems whatsoever.