> My question... What are people's experiences with data retention
> during sleep? Is it reliable? Can it be trusted?

Yes, as long as you maintain the RAM retention voltage of > 1.5V

> So far my values appear to remain intact and I would prefer to not
> stash them in the on board EEPROM. I'm presently running two
> systems as a test, one leaves data in RAM, the other uses the
> EEPROM. After a few hours both are still in sync.

You've also got a heap of FLASH memory available. Nothing
wrong with using EEPROM or FLASH, which will protect your
data from power outages, but you have to watch the write-cycle
endurance. You should verify writes and cycle locations, as 15-
minute re-writes will use up the 1000-write endurance for a
single FLASH location quite quickly, much less so for the EEPROM
(100,000 ) or RAM

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