Update here. A recent data error reminded me that I had used tools/options to move my data in evernote onto a SD card on my surface pro 3. So I bit the bullet, uninstalled and reinstalled, then had to uninstall again as evernote was now insistent that everything HAD to be on the D drive, and finally persuaded it to keep everything on the C drive.
After a few hours now, the experience is worlds away from what it was before. No search pauses, no hangs, and it zips along in an entirely useable fashion.