I need to read up more on it, truthfully. But it seems to me that the Core M chips are basically downscaled iCore chips, all using the same base technology, but not being driven as hard.
As for battery life, it's fairly anecdotal at the moment, but it already seems to be getting better battery performance than my S3 did. On a rough guesstimation, I'd say I'm losing about 10% per hour, which would put it about on par with my old iPad. Though I did notice that when I went to install Photoshop, the download, decompression, and installation hammered the battery fairly hard, dropping it about 5% in 10 minutes.
Now for some benchmarks. I ran Crystal Disk Mark to run 3 passes at 1GB read/write on both the SP4 and my PC. For reference, it's a Haswell i5 4590 with a 512GB Samsung 840 Evo M.2 SSD.
PC
SP4 M3
Going by this, it seems that my SP4 is using a SATA based SSD, rather than the PCI-e based ones used in the upper tier models. It's not slow by any means, considering the niche the M3 model addresses, but it does fall short of what I've seen the i5 and i7 SP4's bench.
And hey, what better way to celebrate spending $1100 on a tablet than by hooking a Xbox 360 controller up through the USB port, and playing some Doom.