Default UleFone / Star u650

Hey guys,

Some time ago I bought a Star / Ulefone U650 because I like the huge screen.

I changed my phone from a Samsung S2 to my U650 but now its a bit slow (not gaming, typing!)
Do you have any ideas, why its stocking while i'm typing an SMS or an Email?

Then I have a second question: There is a MTK6589T builded into the U650 and any
manufacturer has released an CM ROM for their phone with Android 4.4

Could this ROM run on my device too?
Do I have to take care about anything?

Thanks for your answers