5.1.1 to 5.0.2 or 4.4.2

Hello,

I hope it hasn't been answered thousand times already, but with a quick look i can only see the go as stock as it gets way

So, two questions. I have a Cloudy 3.3 5.0.2 backup, but i have installed 5.1.1 CAF roms with loki-ed bootstack (and for other roms, the bumped one) and if i restore the Cloudy backup, i just get an instant view of the LG logo and then a black screen (back-lighted)

a) What is the quickest way to go back to "stock" 5.0.2 roms (eg. Cloudy)?
b) What is the quickest way to go back to "stock" 4.4.2 roms (eg OptimusG3 1.4.1)?

Thanks in advance :)