For my part, will tell you so if you want a fast and software without the "crap" then go ahead and install FXP CM
Stock soft works very well but sometimes you who had a previous unit of cm or fxp.miui etc are just longing for what was on the phone.
I'm not a proponent of playing on the phone but always test a game like GTA III, for example, the Xperia J jams even on the lowest settings, detailed graphics.
Custom ROMs just eliminate this problem
Free Xperia Project
Developer of roms for Xperia:
Xperia X8|Xperia NEO/V|Ray|LWW|Xperia J
Xperia J->4..2>Xpre Blur>Dev ver>unlocked bootloader>CM 10.1
Xperia P >4.3 >unlocked bootloader>CM 10.1
Xperia Z >4.4 >unlocked bootloader>AOSP