There is a rather significant difference with ram preview performance when MP is on versus off. You may want to reconsider that.
I mostly do RAM previews for no more than 0-3 second previews and mostly with MP turned off it renderes much faster for me. And mostly I do some vector graphics animations where there isn't needed much calculations - so it renderes pretty fast with MP=OFF.
Becouse MP does some preparing before rendering. To preview longer pieces (like at least 5 second animations) i turn the MP ON.
So yeah still got the question - does RAM previews with MP=OFF renders Noticeably faster on quad CPU, than dual core CPU. If clock speeds ar similar. (mbp13 vs mbp15)
So i got my answer - I tried to boot with CPUS=1 - so my compter used only one Core (i have a quad core I7 3770). And the render time (21 sec) was exactly the same as with all 4 cores, while doing RAM preview with MP=OFF I did check in MP preferences and it showed that i have only one core available.
Offcourse apps like C4D was day to night compared to using all 4 cores. But it looks like I can easily live with 2 core i5 on laptop.