Generally do you find the Sp4 m3 faster than the Sp3 i5?
The best answer I have right now is, it's probably a little slower. Some of the bugs get in the way of making a solid determination empirically but I haven't really focused on that yet.
PassMark highlights a few things.
Red = SP3 i5 *(selected from their database in roughly the 85-90th percentile ranking)
Blue = SP3 i3 *
Yellow = S3 Atom *
Green = SP4 core m (one run on my SP4)
PassMark Rating: Overall score SP3 i5 edges out the SP4 core m by 9.2% that's not much really.
CPU score SP3 i5 by 23% you could notice that at times.
2D Graphics, SP3 i5 by 50% sounds significant but may be less important than the others. (Intel is focused on 3D graphics).
3D Graphics Here is where the core m out performs the SP3 i5 - down -32%.
Memory is pretty close with 8% difference (not likely noticeable on most things.)
Disk the SP4 comes out ahead.
The SP3 i3 is beaten handily by SP4 core m and the Surface 3 which is hobbled by slow disk is far behind.
I know you have a Surface 3 so that should help you a lot.