[General Questions and Answers] Nazo:
I went to my local RadioShack and held each. In the end, the M7 has a "good enough" processor and feels comfortable in my hand, whereas the M8 is just still bigger than I really want (though it feels more comfortable than my SGS3 at least.) So I guess I'll just get a M7 if I can find one.

You wouldn't happen to know if the micro-USB port supports USB host? I've been under the impression that basically all modern Android devices do, but it would be just my luck if my best possible upgrade option is the one exception...

EDIT:

I'll try to simplify. First, I need the option of a minimal OS with good features built in (CyanogenMod is pretty minimal, but not so much so that they actually remove features and they have some nice stuff built in. I just freeze a few system apps and enjoy the benefits of the extras I actually like and I'm pretty well set with excellent battery life and a beautifully smoothly running device.) Second, it's the closest thing you can really get to "official." With third party ROM builds you might get lucky and still get updates for a long time, but chances are third parties will just forget about it (whereas CM is in some ways almost automatic. You have a maintainer responsible for fixing system-specific issues and if they stop you can get kind of stuck, but I think you still get updates from the current version of CM even if you might not get the next version.) One thing I do know: it has nightlies enabled already for CM12 (aka Android 5.0) so it's definitely not abandoned by a long shot and being better maintained than my SGS3 (which has no CM12 builds under any variant at all, nevermind my d2vzw -- yes, I'm remembering to check d2vzw since they apparently deunified the SGS3 with CM12 for some odd reason mere months after they went to all the trouble to unify towards the end of the CM11 life...) There's also the fact that as long as CM supports something, it's far easier and far more likely that third party builds will actually show up and continue being updated. It's just plain more developed (so bugs are more likely to get squashed) and generally means better overall support and quality will go into the builds. Stock ROMs typically have very limited options (even if they're closer to AOSP without bloatware crap like with Samsung) and are harder to customize to suit one's needs. Stock ROMs also get the least updated... It takes them longer to update and they drop a device sooner (for instance, my SGS3 variant went only up to 4.2... No 5.0 will ever be official for it.) CM may eventually drop a device, but they go much further and unlock much more potential from a device than the manufacturers will do.

PS. Xposed Framework is effectively dead for now. :( It doesn't work on ART and not only is ART better in numerous ways than Dalvik (so I've already been using it on my SGS3 despite having to give up Xposed to do it) but it is required on Android 5.x (Dalvik is removed entirely.) It's also a real pain to do some things using it. For instance, I need a volume fix. It's a real hassle, but I can modify the framework jar to fix the volume to reasonable numbers of steps. There was a module for it, but A. the author went MIA without a word and hasn't updated in positively ages (so if it hasn't stopped working yet, you can bet it will soon) and B. it was exceptionally limited (I want 100 steps and control over each type of volume, not just the main sound and they could only do 30 or 45 on the main control with no ability to separately or even at all control things like BlueTooth and the call volume...) Hopefully Xposed will manage to get ART working (they're on it anyway) but for now you can't count on it. Even if they do (and there are a couple of nice things it can do that I'd love to have back) unless I can learn to program my own modules (doubtful) I still need the extras I can do without it.