hardware platform help

Hi
 
I've been running cakewalk/sonar since the beginning, always on a desktop. I'm currently running x2 with an echo layla interface. I want to move to a laptop, but I'm not sure what the minimum spec is that I need. I'm on a limited budget here.
 
would I be ok with I3 or do I need I5?, and what generation of these would I need. I don't think I can stretch to a new generation I5(7th gen), but maybe a secondhand 4th gen. For the moment I will be running the laptop with a steinberg UR22 until I can afford a proper interface.
 
any help would be appreciated.