Looking at the low end SP4 compared to a Surface 3 Atom.
The SP4 is obviously bigger and heavier but should get much better performance which I find the S3 at times is a little balky (tbh I think the issue with the S3 is mostly bad drivers but it's getting to be more than I can bear) so I'm considering replacing my S3 with a core m3 SP4. Before I can do that they will have to fix Windows 10's Tablet mode which IMO is a sorry touch experience right now.
Here's my performance estimation for a core m3 SP4 compared to Surface 3 Atom.
1. Disk performance on the SP4 will be blazing fast with the PCIe 3.0 SSD compared to eMMC on the Surface 3.
2. Atom vs core m3 there are no current benchmarks for a core m3 but this is an incremental improvement over the Broadwell 5y10 so I'll compare Atom X7-Z8700 to the 5y10
Even with no incremental improvement in the Skylake Core m3 over the 5y10 it will smoke the x7-Z8700 especially with a much faster disk.
I'm willing to trade off the size and weight differential for better performance with the above stated provision. Ideally MS would give us a similarly configured Surface non-Pro Skylake Core m but for now a Core m3 SP4 is slated to replace my S3 and I'll take the better keyboard and pen along with it. I think this configuration of the SP4 will kill the iPad Pro too.