After the failure of the eBay 100F supercaps, I plunked down a few $$ and ordered some from Digikey:
Executive summary: they all performed as expected.
The discharge recovery of the 100F supercap was the worst:
The snap-back was 25mV after more than nearly 7 minutes of rest (and still rising).
The 50F supercaps were stellar -- less than 10mV snap back (but I think they have higher leakage current):
The 25F supercaps were very good as well:
All of these supercaps would work well in the UPS. Real world testing next.