After the failure of the eBay 100F supercaps, I plunked down a few $$ and ordered some from Digikey:

100F +30/-10% manufactured by AVX. 8mΩ ESR. $8/each.

50F +30/-10% manufactured by Illinois Capacitor. 15mΩ ESR. $4/each.

25F +30/-10% manufactured by Eaton. 27mΩ ESR. $4.35/each.

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.