Is this the Freesync 2 monitor to get?

[zinfamous]

Does the monitor itself have an "overdrive" mode or something for the 100Hz?

It does, and you can set it to "weak," "medium," or "strong"
It's found in the "misc" menu, along with:

FreeSync
HDR
Overdriver

Manual is thin on info and doesn't really describe anything. I think I need to sit down with a good online guide about how to use these modern features and what everything means, how it affects the other functions. "HDR" is either off, auto, or smpte 2048. Turning it on just seems to adjust all the levels to produce some ghastly unnatural image that seems to have been filtered for the Rosemary's Baby birth scene.