What's the fasted/most stable rom available (Unrooted) for the 4x HD? topic

I'm getting sick of the lag on my 4x. Camera tags so long the moment has past, messaging crashes 50% of the time, needing the recent tasks to be brought up and cleared before it will work again, browser is infuriating, and whenever anyone calls, the phone will ring and vibrate, but the screen will take so long in bringing up the 'answer/reject' options that sometimes the caller has rung off before I've even had a chance to answer!
This is on the most recent official 4.1.2

I know there's loads of roms available to me, but I need an un-rooted one, as I use the barclays banking app a lot for my business and it won't work on a rooted device.

Is it simple to just turn off the root mode on a custom rom?