well that would be more of a matter of storage, wouldn't it? For burst loads an m3 is basically a previous-gen i5 (ie the 7y30 is similar to an i5-5/6200u for 30 seconds).
I have a SP4 i5 / 4GB and will be getting this upgrade as the enhancements make a good SP even better.
But, will their be a significant difference in performance between the M3 model and i5? I mainly use MS Excel and do not usual have more than 3-4 webpages open at a time. I watch movies (iTunes).
Thoughts? Buy the i5 / 4GB or save £200 and get the M3 version?