For my little useless story I came from galaxy s2 last week and flashed right away 4.2.2 with full wipe.
Was happy of the amazing speed difference with my previous phone and immediately knew this phone was very good.
Then there were some random guys complaining of lags I started to notice too. Nothing too boring but I hoped more from a quad core processor.
So 4 days ago I flashed cwm, made a backup of my precious rom and gave a chance to the "old" 4.3.4 I never tried before.
The speed difference is not at all placebo for me. The system feels definitely much more smoother, but more importantly responsive, all reacts immediately under your fingers.
Yes, I loose some minor extra functionalities but I just prefer my xperia that way. It just works better to me. Added black navbar/status bar, and will center the clock when I will have the time, I must say I am a happy man here and will just pass this 4.2.2 until an update will come out.