I'd get the I7 and maybe put in 16GB of RAM in there, but you have an SSD which boosts speed too. I'd check Autocad's minimum system requirements before you pull the trigger.
I think it may run ok, but the screen size will be limiting. I found working on a 13" laptop with photoshop to be too small. I'd say AutoCad is in the same boat, its an application that really needs a fair amount of screen real estate.