All I know is the i5s in the Microsoft store and there were six of them (all the same apart from type cover) ..three had issues (freezing, disconnect from cursor, error message) . Now of course those were in heavy use and pre-release demo ones but that cannot just be coincidence, three with issues that is 50%....I almost walked out dissapointed but after several hours figured the pre-production demo was part of it and the i5 the other..so went m3.
I think the deal is in the mobile versions of the i series...the i7 gets love so does the m3..its almost as if the i5 is for the masses and the quality is in the other two processors..that is just my opinion but based on actual usage too of both the i5 and the m3 and reading a lot of reviews... yo typically hear i5 has issues the i 7s do not. I love the i5 on my Desktop and my son's SP3 i5 works great but there is something about the i5/SP4 mix that is no bueno.